s3++antisurge

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Antisurge ControlAntisurge Control

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Types of CompressorsTypes of Compressors

• Positive Displacement

• Rotating

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Positive DisplacementPositive Displacement

• Reciprocating (Piston)

• Screw

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RotatingRotating

• Centrifugal

• Axial

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• Widespread use, many applications• Gas is accelerated outwards by

rotating impeller• Can be built for operation as low as

5 psi, or operation as high as 8,000 psi(35 kPa or 55,000 kPa)

• Sizes range from 300 hp to 50,000 hp

Centrifugal compressorsCentrifugal compressors

Single Case Compressor Centrifugal Impeller

IMPELLERS

Picture of horizontal split

Cross section of barrel type compressor

Picture of barrel type compressor

Cross section of bull gear compressor

Picture of (bull) gear and impellers

Picture of bull gear compressor

Cross section of horizontal split

DIFFUSERS

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Compressor inlet nozzle

Thrust bearing

Journal bearing

Shaft and labyrinth seal

Impeller inlet labyrinth seals

Discharge volutes

Impellers

Drive coupling

Casing (horizontally split

flange) Compressor discharge nozzle

Cross section of horizontal splitCross section of horizontal split

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Picture of horizontal splitPicture of horizontal split

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Picture of barrel type compressorPicture of barrel type compressor

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Compressor volutes

Gear casing

Pinion shafts

Journal bearing

Impellers

Drive coupling

Labyrinth seals

Main gear

Inlet guide vanes

Cross section of bull gear compressorCross section of bull gear compressor

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Picture of bull gear compressorPicture of bull gear compressor

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Con

trols

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Picture of (bull) gear and impellersPicture of (bull) gear and impellers

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Axial compressorsAxial compressors

• Gas flows in direction of rotating shaft• Can be built for lower pressures only 10 to

100 psi (0.7 to 6.8 Bar)• High flow rate • Efficient• Not as common as centrifugals

RotorBlades

Casing

StatorBlades

Stator BladesRotor Blades

Casing

Shaft

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Compressor outlet nozzle

Rotor blades

Labyrinth sealsGuide-vane

actuator linkageCompressor rotor

Compressor inlet nozzle Thrust bearing

Adjustable guide vanes

Cross section of axial compressorCross section of axial compressor

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Picture of axial compressorPicture of axial compressor

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Single-Section, Three-Stage Single-Case, Two-Section, Six-Stage

Two-Case, Two-Section, Six-Stage

Series Network

Parallel Network

Compressor system classificationsCompressor system classifications

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Developing the compressor curveDeveloping the compressor curve

Pd Discharge Pressure (P2)ΔPc Differential Pressure (Pd - Ps) or (P2 - P1) Rc Pressure Ratio (Pd/Ps) or (P2/P1) Hp Polytropic Head

Rc

Qs, normalQs, massQs, vol

Compressor curve for a specific

speed N1

Rprocess,1

Q1

Rc1

Rprocess,2

Q2

Rc2

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Stable zoneof operation

Developing the compressor curveDeveloping the compressor curve

Minimum speed

Power limit

Maximum speed

Process limit

Qs, vol

Adding control margins

Stonewall orchoke limit

Surge limit

Rc

Actual availableoperating zone

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What is Surge?What is Surge?

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Key Issues on Turbomachinery Controls

Key Issues on Turbomachinery Controls

• Energy consumed by turbomachinery is a major cost of operation in process plants and oil production operations

• Poor control is a major risk to the safe and reliable operation of turbomachinery

• The economic consequences of non-availability of turbomachinery is large

• Poor control can lead to false limitations on production

• Capable support services are critical to the successful application of turbomachinery controls

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Surge descriptionSurge description

• Flow reverses in 20 to 50 milliseconds• Surge cycles at a rate of 0.3 s to 3 s per

cycle• Compressor vibrates• Temperature rises• “Whooshing” noise• Trips may occur• Conventional instruments and human

operators may fail to recognize surge

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Some surge consequencesSome surge consequences

• Unstable flow and pressure• Damage in sequence with increasing

severity to seals, bearings, impellers, shaft• Increased seal clearances and leakage • Lower energy efficiency• Reduced compressor life

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Factors leading to onset of surgeFactors leading to onset of surge

• Startup• Shutdown• Operation at reduced throughput• Operation at heavy throughput with:

– Trips– Power loss– Operator errors– Process upsets– Load changes– Gas composition changes– Cooler problems– Filter or strainer problems– Driver problems

• Surge is not limited to times of reduced throughput.

• Surge can occur at full operation

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• Rapid flow oscillations • Thrust reversals• Potential damage

FLOW

PRESSURE

TEMPERATURE

TIME (sec.)1 2 3

TIME (sec.)1 2 3

TIME (sec.)1 2 3

Major Process Parameters during Surge

Major Process Parameters during Surge

• Rapid pressure oscillations with process instability

• Rising temperatures inside compressor

Operators may fail to recognize surge

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• From A to B…….20 - 50 ms…………….. Drop into surge• From C to D…….20 - 120 ms…………… Jump out of surge• A-B-C-D-A……….0.3 - 3 seconds……… Surge cycle

Qs, vol

Pd

Machine shutdownno flow, no pressure

• Electro motor is started• Machine accelerates

to nominal speed• Compressor reaches

performance curveNote: Flow goes up faster because pressure is the integral of flow

• Pressure builds• Resistance goes up• Compressor “rides” the curve• Pd = Pv + Rlosses

Pd = Compressor discharge pressurePv = Vessel pressureRlosses = Resistance losses over pipe

Developing the surge cycle on the compressor curve

Developing the surge cycle on the compressor curve

Pd

Pv

Rlosses

B A

CD

• Compressor reaches surge point A• Compressor loses its ability to make pressure• Suddenly Pd drops and thus Pv > Pd• Compressor surges -“Plane goes to stall”• Because Pv > Pd the flow reverses• Compressor operating point goes to point B• Result of flow reversal is that pressure goes down• Pressure goes down => less negative flow• Operating point goes to point C• System pressure is going down• Compressor is again able to overcome Pv• Compressor “jumps” back to performance curve and goes to

point D• Forward flow is re-established• Compressor starts to build pressure• Compressor “rides” curve towards surge• Point A is reached• The surge cycle is complete

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How far away are we from Surge?

How far away are we from Surge?

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Calculating the distance between the SLL and the compressor operating point

Calculating the distance between the SLL and the compressor operating point

The Ground Rule– The better we can measure the distance to surge, the

closer we can operate to it without taking riskThe Challenge

– The Surge Limit Line (SLL) is not a fixed line in the most commonly used coordinates. The SLL changes depending on the compressor inlet conditions: Ts, Ps, MW, ks

Conclusion– The antisurge controller must provide a distance to surge

calculation that is invariant of any change in inlet conditions

– This will lead to safer control yet reducing the surge control margin which means:

• Bigger turndown range on the compressor • Reduced energy consumption during low load conditions

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Commonly used (OEM provided) coordinate systems of the compressor map

Commonly used (OEM provided) coordinate systems of the compressor map

• Typical compressor maps include: (Qs, Hp), (Qs, Rc), or (Qs, pd) coordinates, where:

Qs = Suction flow and can be expressed as actualor standard volumetric flow

Hp = Polytropic HeadRc = Compressor Ratio (pd / ps)pd = Discharge pressure of the compressorps = Suction pressure of the compressorks = Exponent for isentropic compression

• These maps are defined for (1) specific set of inlet conditions: ps, Ts, MW and ks

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• These coordinates are NOT invariant to suction conditions as shown

The problem with OEM providedcoordinate systems of the compressor map

The problem with OEM providedcoordinate systems of the compressor map

• For control purposes we want the SLL to be presented by a single curve for a fixed geometry compressor

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NOT invariant coordinates (Hp, Qs) Invariant coordinates (hr, qr2)

where:Hp = Polytropic headQs = Volumetric suction flowhr = Reduced headQr

2 = Reduced flow squared

Understand the limitations of mapsUnderstand the limitations of maps

•Choose the right coordinates for the antisurge control system

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Coordinates (Rc ;Qs) and (Rc ;qr2)Coordinates (Rc ;Qs) and (Rc ;qr2)

NOT invariant coordinates (Rc, Qs)

qr2

Invariant coordinates (Rc, qr2)

where:Rc = Pressure ratioQs = Volumetric suction flowQr

2 = Reduced flow squared

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Coordinates (Rc ;jr) and (Rc ;Ne2)Coordinates (Rc ;jr) and (Rc ;Ne2)

Invariant coordinates (Rc, jr) Invariant coordinates (Rc, Ne2)

where:Rc = Pressure ratiojr = Reduced powerNe

2 = Equivalent speed squared

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• A coordinate system that is invariant to suction conditions is:

hH

(ZRT)rp

s= and q

QZRTr

s

s

=( )

• Squaring the flow will still keep coordinates invariant:

hH

(ZRT)rp

s= and q

QZRTr

s

s

22

=( )

increasing MW, N

decreasing T s

qr2

hr

Representing the SLL as a single curve using reduced coordinatesRepresenting the SLL as a single curve using reduced coordinates

Design Nitrogen Off-gasMW MW MWPs Ps PsTs Ts Tsks ks ks

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qr2 =

Qs2

(ZRT)s

where:R = Ru / MWRu = Universal gas constantR = Specific gas constantMW = Molecular Weight of the gasps = Suction pressureK = Orifice plate constantΔpo,s = Differential pressure across orifice plateTs = Temperature of the gas in suctionZs = Compressibility of gas in suction of compressor

=

K . Zs. Ru

. Ts

MW Δpo,s.

ps

(ZRT)s

= Δpo,s

ps

The antisurge controller calculates qr2 using ps and Δpo,s

transmitters

Calculating qr2 (reduced flow squared)Calculating qr2 (reduced flow squared)

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hr = Hp

(ZRT)s

where:R = Ru / MWRt = Td / Ts Temperature ratioRc = pd / ps Pressure ratio Ru = Universal gas constantR = Specific gas constantMW = Molecular Weight of the gasPd = Discharge pressureps = Suction pressureZs = Suction compressibilityσ = Exponent for polytropic compression

=

Zs. Ru

. Ts

MW Rc

σ-1. σ

(ZRT)s

= Rc

σ-1σ

The antisurge controller calculates hr using pd, ps, Td and Tstransmitters

log(Rt)log(Rc)

For polytropic compression Rt = Rcσ thus σ =

Calculating hr (reduced head)Calculating hr (reduced head)

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Calculating Reduced functions

We can reduce the equations even further by removing the constants

= Ss = K .Hp

Qs2

Ss = K

Rcσ-1σ

Δpo,s

ps

.

Zave. Ro

. Ts

MW Rc

σ-1σ

.

Zs. Ro

. Ts

MW Δpo,s.

ps

K .

The result is reduced equations for Polytropic Head Reduced (hr) and Suction Flow Reduced (qr

2) :

• where:• hr = and qr

2 =Rc

σ-1σ

Δpo,s

ps

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The relationship between pressure and temperature for polytropic compression is:

Calculating σ improves accuracy when:- Gas composition varies- Compressor efficiency changes

Solving for σ:

σ can be calculated from Pressure and Temperature Measurements

σ can be calculated from Pressure and Temperature Measurements

Ts

σTd = = σ⎛ ⎞

Ps

Pd

⎝ ⎠ Rc

⎝ ⎠

⎝ ⎠σ =log

log

⎛ ⎞Ts

Td

⎛ ⎞Ps

Pd

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• The surge parameter is defined as: S f

qsr

r op= 1

2(h )

,

• The function f1 returns the value of qr2 on

the SLL for input hr

hr

qr,SLL2

• Non-linearity in the Surge Limit Line can be accommodated using a function based on a piecewise characterization of either map axis qr

2

hr

Building the Surge Limit LineBuilding the Surge Limit Line

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qr2

hr

qr,op2

• The function f1 returns the value of qr on the SLL for input hr

2

hr

qr,SLL2

• As a result: Ss = qr,op2

qr,SLL2

OP

OP = Operating Point

• Ss < 1stable operating zone

Ss < 1• Ss = 1

surge limit line (SLL)

Ss = 1

• Ss > 1surge region

Ss > 1

The surge parameter SsThe surge parameter Ss

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Introducing the distance between the operating point and the Surge Control Line

Introducing the distance between the operating point and the Surge Control Line

• Step 1 Introduce parameter: d = 1 - Ss

qr2

hr

Ss < 1

Ss > 1

Ss = 1d = 0

d > 0

d < 0

• Step 2 Introduce parameter: DEV = d - surge margin

DEV = 0

Surge margin

DEV > 0

DEV < 0

• The parameter DEV is independent of the size of the compressor and will be the same for each compressor in the plant

- Operating Point

Benefits:One standard surge parameter in the plantNo operator confusion:

DEV > 0 GoodDEV = 0 Recycle LineDEV < 0 Bad

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Antisurge Control . . .Antisurge Control . . .

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Surge parameter based on invariant coordinates Rc and qr

– Flow measured in suction (ΔPo)– Ps and Pd transmitters used to calculate Rc

1UIC

VSDS

Compressor

1FT

1PsT

1PdT

• The antisurge controller UIC-1 protects the compressor against surge by opening the recycle valve

DischargeSuction

• Opening of the recycle valve lowers the resistance felt by the compressor

• This takes the compressor away from surge

Basic Antisurge Control SystemBasic Antisurge Control System

Rc

qr2

Rprocess

Rprocess+valve

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A

Rc

B • When the operating point crosses the SCL, PI control will open the recycle valve

• PI control will give adequate protection for small disturbances

SLL = Surge Limit LineSCL = Surge Control Line

qr2

Antisurge Controller Operation Protection #1 The Surge Control Line (SCL)

Antisurge Controller Operation Protection #1 The Surge Control Line (SCL)

• PI control will give stable control during steady state recycle operation

• Slow disturbance example

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Con

trol

s Cor

por

atio

n

• b = (b1) + (b2 x n) + (b3 x Td0 x dSs/dt)

The b equationThe b equation

• b = (b1) + (b3 x dSs/dt)

• dSs/dt is the velocity of the operating point

• It is the measurement of the stability of the process

• -1 <= dSs/dt <= +1

• Positive is movement towards surge

• Negative is movement away from surge

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Adaptive Gain Enhancing the Effectiveness of the PI Controller

Adaptive Gain Enhancing the Effectiveness of the PI Controller

A

Rc

B

• When the operating point moves quickly towards the SCL, the rate of change (dS/dT) can be used to dynamically increase the surge control margin.

• This allows the PID controller to react earlier.

• Smaller steady state surge control margins can be used w/o sacrificing reliability.

• Fast disturbance exampleQ2

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What affects the value of b1?What affects the value of b1?

• Stroking speed of the valve

• Capacity of the valve

• Discharge volume to upstream ofantisurge valve

• Suction volume to downstream of antisurge valve

• Shape of compressor curves

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Con

trol

s Cor

por

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What does Td0 do?What does Td0 do?

• Td0 acts like a multiplier for dSs/dt

• It simply makes the controller more sensitive or less sensitive to changes or disturbances in the process

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Antisurge Controller Operation Protection #2 The Recycle Trip® Line (RTL)

Antisurge Controller Operation Protection #2 The Recycle Trip® Line (RTL)

Benefits:– Reliably breaks the

surge cycle– Energy savings due to

smaller surge margins needed

– Compressor has more turndown before recycle or blow-off

– Surge can be prevented for virtually any disturbance

SLL = Surge Limit LineSCL-2 = Open Loop Line

SCL = Surge Control Line

Output to Valve

Time

Open-loop Response

PI Control Response

PI Control Recycle Trip®

Action

+

To antisurge valve

Total Response

Rc

Q2

OP

• Disturbance arrives - the operating point moves towards the SCL• When the operating point reaches the SCL, the PI controller opens the

a/s valve based on it’s proportional and integral action.• The operating point overshoots the SCL until it reaches RTL• When the operating point hits RTL the conclusion is:

– We are close to surge– The PI controller is too slow to catch the disturbance– Move the valve now!

• An open loop response is triggered• Operating point moves back to the safe side of RTL

– The Open-loop function should be ramped out– PI controller integrates to stabilize the operating point on the

SCL• Total response of the controller is the sum of the PI control and the

Recycle Trip® action

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Improving the accuracy of Recycle Trip®

open loop controlImproving the accuracy of Recycle Trip®

open loop control

• Recycle Trip® is the most powerful method known for antisurge protection

• But, open loop control lacks the accuracy needed to precisely position the antisurge valve

• Open loop corrections of a fixed magnitude (C1) are often either too big or too small for a specific disturbance

• The rate of change (derivative) of the compressor operating point has been proven to be an excellent predictor of the strength of the disturbance and the magnitude required from the Recycle Trip®

response• Therefore, the magnitude of actual step (C) of the

Recycle Trip® response is a function of the rate of change of the operating point or d(Ss)/dt

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Output to valve

Time

Medium disturbance

PI ControlRecycle Trip®

Total

Large disturbanceOutput to valve

Time

PI Control

Recycle Trip®

Total

Benefits• Maximum protection

– No surge– No compressor damage

• Minimum process disturbance– No process trips

Recycle Trip®

Response calculation:

100%

0%

Recycle Trip® based on derivative of SsRecycle Trip® based on derivative of Ss

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After time delay C2 controller checks if Operating Point is back to safe side of Recycle Trip® Line- If Yes: Exponential decay of Recycle Trip® response.

Output to valve

Time

One step response

PI ControlRecycle Trip®

Total

100%

0%

C2

Multiple step responseOutput to valve

Time

PI Control

Recycle Trip®

Total

C2 C2 C2

What if one Recycle Trip® step response is not enough?

What if one Recycle Trip® step response is not enough?

- If No: Another step is added to the Recycle Trip® response.

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Additional surge margin

Benefits of Safety On® response:Continuous surging is avoidedOperators are alarmed about surge

• Compressor can surge due to:– Transmitter calibration

shift– Sticky antisurge valve

or actuator– Partially blocked

antisurge valve or recycle line

– Unusually large process upset

Antisurge Controller Operation Protection #3The Safety On® Response (SOL)

Antisurge Controller Operation Protection #3The Safety On® Response (SOL)

Rc

qr2

SLL - Surge Limit LineRTL - Recycle Trip® LineSCL - Surge Control Line

New SCL

New RTL

SOL - Safety On® Line

• Time-Based Safety On Response• Safety On Reset

If the Operating Point Crosses the Safety On® Line the compressor is in surgeThe Safety On® Line the compressor is in surge surgeThe Safety On® response shifts the SCL and the RTL to the rightAdditional safety or surge margin is addedPI control and Recycle Trip® will stabilize the machine on the new SCL

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Built-in surge detectorBuilt-in surge detector

Pressure and Flow Variations During a Typical Surge Cycle

100%

100%

0%

0%

Pd

ΔPo

20 to 50 milli-seconds

1 TO 2 SECONDS

• Surge signature should be recorded during commissioning.

• Rates of change for flow and pressure transmitters should be calculated.

• Thresholds should be configured slightly more conservative than the actual rates of change during surge.

• Surge is detected when the actual rates of change exceed the configured thresholds

• The following methods have been used:– Rapid drops in flow and pressure– Rapid drop in flow or pressure– Rapid drop in flow only– Rapid drop in pressure only

• When surge is detected a Safety On®

response is triggered• A digital output can be triggered upon a

configurable number of surge cycles

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1UIC

VSDS

Compressor

1FT

1PsT

1PdT

• The antisurge controller can be configured to limit:- Maximum discharge pressure (Pd)- Minimum suction pressure (Ps) - Both maximum Pd and minimum Ps

• This does NOT conflict with antisurge protection

DischargeSuction

Limiting Ps or Pd using the Antisurge Controller

Limiting Ps or Pd using the Antisurge Controller

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Disturbance comes from the discharge sidePd,2 increasesPs,2 remains constantRc,2 increasesSection 2 moves towards surge

Antisurge UIC-2 will open the recycle valve to protect section 2 against surge

Pd,2 decreasesPs,2 increasesRc,2 decreasesSection 2 moves away from surge

Opening of recycle valve on section 2 caused Ps,2 = Pd,1 to increase Result:

Pd,1 increasesPs,1 remains constantRc,1 increasesSection 1 moves towards surge

Antisurge controller UIC-1 will open the recycle valve to protect section 1 against surge

Pd,1 decreasesPs,1 increasesRc,1 decreasesSection 1 moves away from surge

Opening of recycle valve on section 1 caused Pd,1 = Ps,2 to decreaseResult:

Ps,2 decreasesPd,2 remains constantRc,2 increasesSection 2 moves towards surge

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Disturbance

Interacting Antisurge Control LoopsInteracting Antisurge Control Loops

Rc,2

qr,22

RRc,1

qr,12

R

RR

1PIC

2UIC

1UIC

VSDS

Section 1 Section 2

• The system is oscillating• Slowing down the

controller tuning would lead to:- Increased risk of surge

• Compressor damage• Process trips

- Bigger surge margins• Energy waste

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tion • All CCC controllers are connected on a serial network

1PIC

2UIC

1UIC

VSDS

Section 1 Section 2

Serial network

Serial network

• This allows them to coordinate their control actions• When UIC-2 opens the recycle valve:

- Section 2 will be protected against surge- Section 1 will be driven towards surge

• How much section 1 is driven towards surge depends on how much the recycle valve on section 2 is opened

• The output of UIC-2 is send to UIC-1 to inform UIC-1 about the disturbance that is arriving

• UIC-1 anticipates the disturbance by immediately opening its valve

Note: The same applies when the antisurge valve on section 1 is opened first

Loop Decoupling between multiple Antisurge Controllers

Loop Decoupling between multiple Antisurge Controllers

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Fall-back strategiesFall-back strategies

• Antisurge controller– If a pressure transmitter fails, a minimum q2r

algorithm is used– If a temperature transmitter fails, hr is

characterized as a function of compression ratio

– If the speed transmitter fails, a conservative speed setting is used

– If the flow transmitter fails• Redundant transmitter is used• Output is driven to:

– Last value OR– Last Value selected: If Last Value >Pre-selected fixed

value ORPre-selected fixed value selected: If Pre-selected fixed value>Last Value

• All transmitter failures are alarmed

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Controller output

Flow ratethrough

valve

Valve trim

quick opening

Controller output

Notes• Used to improve controllers operation

when non-linear valves are used• Used on retrofits to avoid additional investment in new valve• Works well with equal percentage characteristics• Works less satisfactory with quick opening characteristics

• For antisurge control a linear valve is preferred

• Linear valve gives the same dynamic flow response over its complete stroke

• Existing valve has equal percentage trim

• Controller output is characterized as mirror image in the linear valve line

• Dynamic flow response becomes linear

• Existing valve has quick opening trim

• Controller output is characterized as mirror image in the linear valve line

• Dynamic flow response becomes linear

Valve trimequal percentage

Controller output

Output linearizationOutput linearization

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Controlleroutput

Flow ratethrough

valve

0% to the valveLow clamp on controller output

Dynamic control range

TSL = Tight Shut-off Line

B

Rc

qr2

SLL RTLSCLSOL

C

PI Control

Benefits• No leakage and noise when controller

is far away from surge - point A• Eliminates noise and energy waste• Eliminates dead time in the response

of the antisurge valve when the operating point is close to the SCL

Controlleroutput

The Tight Shut-off Line (TSL)The Tight Shut-off Line (TSL)

A

A Time

BC

• Many antisurge valves have the following characteristic:• from 0% to low clamp value the flow rate through the valve is

(almost) zero and does not change• Once the low clamp is reached the characteristic is linear• Typical low clamp value can be 5% - we will use the 5% as the

value throughout in this example• For dynamic control we want to use the range 5% - 100% on the

valve• The 5% or low clamp value represents the closed position for control

purposes• At the low clamp value the valve

• Usually still leaks which results in energy waste• Makes an annoying noise

• Typical for worn valves and valves with Teflon seat• CCC antisurge controller has a Tight Shut-off Line (TSL) that eliminates

the disadvantages• When the operating point is to the right of the TSL the controller closes

the valve at 0% - point A• This is below the low clamp value• When the controller crosses the TSL the output of the controller jumps

to the low clamp value - point B• The controller is now “ready to go” when the operating points hits the

SCL - point C

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Manual Override - MORManual Override - MOR

• MOR = “On” is called Hard Manual.• MOR = “Off” is called Soft Manual.• The correct setting of MOR is normally

“Off”.• With MOR = “Off”, controller will switch

from Manual to Auto when Operating Point crosses the RTL, and will bring the Operating Point back to the SCL.

• With MOR = “On”, controller is nothing but an open-and-close button for your antisurge valve. The controller ignores the calculation of DEViation and gives no surge protection whatsoever.

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• Normally, the Antisurge Controller will transfer from MANUAL to AUTOMATIC operation when the operating point of the compressor crosses the Recycle Trip Line.

• The MOR function allows MANUAL to override this feature.

• Manual override is normally set to OFF.• Manual override must be ON for “Hard Manual” operation.

RTLSLL SCL

ΔPC

Manual Override -hard_manual_enable

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Do I turn it ON or OFF?Do I turn it ON or OFF?

DON’T BE A MORON . . .

DON’T LEAVE MOR ON !

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Series 3++ Antisurge ControllerFace Display

The three-digit DEV readout usually displays the three-digit deviation of the operating point from the Surge Control Line. Positive values indicate an acceptable margin of safety, negative values indicate unsafe operation.

The three-digit SP readout is normally blank.

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The three-digit OUT readout normally displays the recycle or blow-off valve Actuator Control Signal :• When using Output Reverse, OUT

will display 100 minus the ACS so it always reflects the intended percent open position of the valve.

• When using Valve Dead Band Compensation, the displayed value will jump by more than the intended change in the valve position when that control response reverses.

• In a Valve Sharing application, the intended valve position is displayed only by the primary Antisurge Controller. The OUT readouts of all secondary controllers are blank.


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If the ALT button is held down:

• The OUT readout displays the antisurge control response, which is the intended percent-open position of the recycle or blow-off valve prior to any output transformations.

• The DEV readout displays half the denominator of the configured proximity-to-surge Application Function, and

• The SP readout displays half of that function’s numerator.

These alternate DEV (flow) and SP (head) readouts also indicate how closely the compressor is operating to its surge limit. When using fA Mode 31, for example, DEV will display ΔPo,c/2 and SP will display K· f1 (Rc)·Ps/2. If that DEV is below that SP, the compressor is either in surge or the controller is incorrectly tuned.


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If the LIMIT 2 or LIMIT 3 button is held down, DEV and SP will temporarily display the corresponding limiting variable and its control threshold.

Either loop’s variables are usually displayed using the same scaling as its measured variable. However, if either loop is limiting a pressure calculated from the pressure rise across the compressor, its readouts are scaled as percentages.

If either variable is beyond its control threshold, the Limit LED in the lower section of the front panel will be lit and the output signal will be automatically increased to return that variable to an acceptable level.


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Pressing the MENU button displays the most-recently selected screen from the next enabled menu. If the last menu is active, it will display a screen from the first menu.

If the current menu includes more than one screen, pressing the SCROLL button displays the next one. If that menu is displaying its last screen, it will cycle back to the first.

The Acknowledge (ACK) button is not used by the compressor control applications.

Series 3++ Antisurge ControllerMenu System Buttons

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One of these two LEDs will always be lit:

• The green LED in the AUTO key indicates automatic operation. It flashes if the default output fallback strategy is active.

• The yellow LED in the MAN key indicates manual operation. It flashes when operating in manual with Manual Override enabled (no automatic protection).

Series 3++ Antisurge ControllerControl Keys

Pressing either key while its LED is off will toggle the controller to that mode of operation and light that LED. Automatic or manual operation can also be selected via serial communications.

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Vary the actuator control signal when manual operation is selected. Momentarily pressing the Raise key will increment that signal by 0.1 percent, while holding it down increases the output in steadily larger increments (it takes about 20 seconds to change the control signal by a full 100 percent). The Lower key reduces the output in a similar fashion.

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If the Safety On Response detects an actual surge, the controller increments the surge count (which can be viewed via the Main Status Menu) and increases the surge control margin. The red LED in the SURGE RESET key is lit whenever that count is greater than zero, and pressing that key resets that count to zero.


CAUTION!!!To avoid repeated surging, do not press the SURGE RESET key while its LED is lit unless the causes of the surging have been identified and corrected.

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If the controller is being manually operated, the yellow RT LED is lit when the margin of safety falls below the threshold for the Recycle Trip Response, and stays lit only until an adequate margin of safety is restored. When operating automatically, the RT LED remains lit until the Recycle Trip response decays to zero, even if an adequate margin of safety has been restored.

Series 3++ Antisurge ControllerFace LEDs

The yellow POC LED is lit when the recycle flow rate is elevated by the Performance Override control feature.

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• Output Tracking is active, or

• The Remote Low Output Clamp is above the internal Low Output Clamp, even if it has not caused an increase in the recycle rate.

The green Tracking LED will flash to indicate either:

When redundant controllers are installed, the tracking controller will light this LED and that of the active controller (the one protecting the compressor) will either be off or flash to indicate speed tracking.

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The yellow Limit LED is lit when either Recycle Limiting variable is beyond its control threshold, which will increase the recycle rate above the level needed for surge protection alone.

Pressing the LIMIT 2 or LIMIT 3 button in the control loop readout section will display the corresponding loop’s process variable and limiting control threshold.

The green Balance LED is lit when the Recycle Balancing feature is enabled and active (for example, initiating manual control would extinguish it). It does not indicate that feature has actually changed the intended recycle flow.

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The yellow Fallback LED is lit when one of the controller’s Fallback Strategies is being used to calculate proximity to surge, usually because a required analog or serial input has failed.

The red Stop LED is lit when the antisurge controller is operating in its Stop or Purge Operating State, in which case it holds its control valve in a configured position and manual operation might not be permitted

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Series 3++ Antisurge ControllerStatus LEDs

The red Fault LED lights, the status screen displays “No Comms with Main CPU”, and all other display elements turn off if the engineering panel is unable to communicate with the CPU. This usually means the control program is no longer executing and an alternate means of control should be immediately activated.

The yellow Alarm LED lights whenever the controller is experiencing any of the problems that can be indicated via the Alarms Menu. It turns off when all such problems have been corrected.

CAUTION!!!If the Fault LED lights or any Fault relay de-energizes, the analog output signal should be immediately disconnected from its control element (the connected circuits often include relays that do so).

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Series 3++ Antisurge ControllerStatus Screen

Each line of the status screen can display up to ten letters, digits, or other symbols:

• The top line always displays the Application Operating State.

• The remaining three lines display various sets of controller status variables or operator prompts, which are selected by pressing the Menu System Buttons

The contrast of this screen can be adjusted from the Testing and Options Menu

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Series 3++ Antisurge ControllerStatus Screen

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Series 3++ Antisurge ControllerMain Status Menu

Initially, the fourth line will be blank while the second and third lines display the Total B variable, which is the distance between the surge limit and the Surge Control Line, and the number of surges counted by the Safety On Response. The next press of the SCROLL button would display the states of all seven digital inputs and all five digital outputs:

then

Digits indicate the corresponding inputs and outputs are asserted or energized, underscores indicate they are cleared. The 1 for fault relay CR1 will appear unless it (and possibly CR2) are de-energized by CR1’s assigned function. In the above example, only the D2 and D6 inputs are asserted, and only the CPU/IO PCB fault relays and CR4 should be energized.

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The next two presses of the SCROLL button will then display the intended and measured values of the analog outputs:

The next two presses of the SCROLL button will display the actual CPU/IO PCB component power voltages:

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The next press of the SCROLL button will display the controller’s internal temperature:


Subsequent presses of the SCROLL button would repeat the above status screens.

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Series 3++ Antisurge ControllerAnalog In Menu

Pressing the MENU button while any of the above screens is visible will display the scaled value of one analog input on the fourth line, below its configurable eight-character name on the third line:

If an input’s unscaled value is within its acceptable range, a user-defined engineering units label will appear after its scaled value (as shown to the left above). If not, the word “Fail” will be displayed, the Alarm LED will be lit, and the Alarms Menu will indicate “Tran”.

Pressing SCROLL repeatedly will cycle through the screens for all of the enabled Measured Variables.

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Series 3++ Antisurge ControllerCalculated Variables Menu

Pressing the MENU button while any of the above screens is visible will display one of the controller’s independently enabled or disabled Calculated Variable Screens:

Pressing the SCROLL button will cycle through the enabled screens, each of which displays one or two of these variables:• Sigma and Hpr are the Polytropic Head Exponent and Reduced Head,

which are displayed on one screen (as shown above).

• Rc is the Compression Ratio.

• Rt is the discharge to suction Temperature Ratio.

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• Flow is the pressure- and temperature-compensated Displayed Flow, which is calculated from the measured or estimated pressure dropacross an orifice plate.

• UsrQ is the Displayed Net Flow, which is calculated by subtracting a calculated recycle flow from the Displayed Flow.

Series 3++ Antisurge ControllerCalculated Variables Menu

In the event that one or more of the inputs used to calculate these variables fail, the controller can substitute default values for either those inputs or the calculated variable.The resulting fallback value would then be displayed.

• Speed is the Displayed Speed, usually scaled to rpm.

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Series 3++ Antisurge ControllerAlarm Menu

Pressing the MENU button while any of the above screens is visible will display the health of the analog inputs, recycle valve output, intercontroller communications, and CPU/IO PCB voltages:

Each problem’s abbreviation is displayed only if it exists:

• If “Tran” appears on the left side of the third line, one or more analog inputs are beyond their acceptable ranges. The failed input(s) can be identified by scrolling through the Analog In Menu.

• If “OutF” appears on the right side of that line, the intended and measured values of OUT1 (or both OUT1 and 2 if the split output is enabled) differ by more than 5.0 percent.

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• If one of the following appears on the left side of the fourth line, the controller has failed to detect expected intercontroller communication activity on the corresponding serial port:

Series 3++ Antisurge ControllerAlarms Menu

“Comm1” indicates transmissions are not being received from a controller.

“Comm2” indicates transmissions are not being received from a load-sharing or performance override master, while

“Com1&2” indicates both problems exist at the same time.

• If “24V” appears on the right side of the fourth line, the power supply is not providing an acceptable voltage to the CPU/IO PCB. If “15V”, “5V”, or “3V” is displayed there, the voltage from the corresponding power converter is below its acceptable minimum, and the CPU/IO PCB needs to be replaced.

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Series 3++ Antisurge ControllerFunctions Menu

Pressing the MENU button while the above display is visible will display the argument and computed values of one of this controller’s Characterizing Functions:

• The Y Coordinate Characterizer defines the surge limit in the primary coordinate system (that is, the minimum value of X as a function of Y).

• The Reported Flow Characterizer defines the reported flow measurement sent to companion controllers in multisection compressor applications.

• The X Coordinate Characterizer usually defines the X primary coordinate as a function of speed.

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Series 3++ Antisurge ControllerFunctions Menu

• The General Characterizer defines the surge limit as a function of the secondary coordinate variable specified by the f5 Argument.

• The Balancing Variable Characterizer defines the series load-balancing variable (L) as a function of the Load Balancing Variable.

• The Recycle Flow Characterizer defines the recycle flow rate as a function of the control response(used for series load balancing and net flow calculations).

If a particular characterizer is not being calculated, its argument and result values will display as a series of hyphens (“–.– –”). Displaying any one of them allows you to SCROLL to the others, and the last one displayed is the first shown the next time you invoke this MENU.

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Series 3++ Antisurge ControllerTesting & Options Menu

Holding the TEST key down invokes the Display Testing and Options menu:

where the # characters represent the digits of the installed version of the front-panel firmware. You must continue to hold the TEST key down while scrolling through and using any of the following tests.

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The first press of the SCROLL button invokes the procedure for adjusting the contrast of the status screen’s liquid crystal display:

Unless this contrast is already set to its highest (or lowest) level, it will then be slightly increased (or decreased) each time you press the Raise (or Lower) key.

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The second press of the SCROLL button invokes a display from which you can brighten or dim the control loop readouts:

Unless the readouts are already brightened (or dimmed), pressing the Raise (or Lower) key will then make them brighter (or dimmer).

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The third press of the SCROLL button initiates the LED Test, which displays the following message and turns on every numeric readout segment and LED on the Front and Engineering Panels:

s3++antisurge

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