getting the most from your sensors and transducers · 2012-03-23 · getting the most from your...

Getting the Most from

your Sensors and

Transducers

How to make fast, reliable

sensor measurements with

your data logger system

Presenter: Mark D. Bailey

Product Marketing Manager

Modular Data Acquisition and Switching Platforms

Agilent Technologies

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© Agilent Technologies, 2012

Reliable Measurement of Sensors/Transducers

In this seminar, we will cover:

1. Common Sensor Types; their advantages and disadvantages

2. Techniques to reduce Sources of Error and Noise

3. Interfacing Transducers to a Data Logging System

4. Using a Web Interface to quickly set up & debug a Data Logger

5. Fast and easy instrument control and automation using Agilent’s Command Expert S/W

At the end of the seminar, you should be able to:

1. Select the correct sensors for your application

2. Reduce measurement errors due to noise and other factors

3. Identify the necessary characteristics/specs for your data logger system

4. Recognize the benefits of an instrument’s built-in web server and data logging software

5. See the benefits of Agilent’s Free Command Expert Software

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Data Logger System Architecture

Transducer Signal

Conditioning Multiplexer

Digital

Multimeter

(DMM)

Display

Analysis &

Reporting

A/D 28.32 C MON

VIEW

SCAN

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…and we will also touch on these Our focus today …

Data Logger Systems - Transducers

• Temperature

• Flow

• Pressure

• Strain

• Position

• Weight

• Speed

Transducer

DC Volts

AC Volts

DC Current

AC Current

Resistance

Frequency

Physical Parameters Electrical Signals

Transducers or sensors convert a physical phenomena to an electrical signal

• Choose the correct sensor • Mount it correctly • Position it correctly

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Agilent Application Note 290:

“Practical Temperature Measurements”

5 © 2012 Agilent Technologies

US Distribution Training March 2012

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Physical Transducers

Rotation Linear Voltage Displacement Transducer (LVDT)

Pressure Strain Temperature

Temperature Sensors

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Thermistors

Galileo Thermometer

RTDs

Thermocouples

IC Sensors

Agilent Application Note, “How to Select the Correct Temperature Sensor”

http://cp.literature.agilent.com/litweb/pdf/5990-9793EN.pdf

Thermocouples

Thermocouples made from two Dissimilar Metals

(e.g.; Iron and Constantan)

• J-type thermocouple @ room temp < 1mV

• A 1 C change at 0 C = 50.38 V

• To see a 0.1 C change in a J-type thermocouple at 0 C, your instrument must be able to resolve down to 5 V.

VAB + -

Metal A

Metal B

Watch for: • Good junctions • Thermal shunting • Noise and leakage current • Thermocouple specs • Calibration of TC

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• Create a reference junction

• Measure Tref using a thermistor

• Lookup Vref for Thermocouple

at reference junction

• Compute Vx = V+Vref

• Solve for Tx using Vx

0 Tref

Vx

Vref

Tx

V

o

How to measure a Thermocouple

Tref

VX

Metal A

Metal B

Metal C

Metal C

V +

-

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Need sufficient resolution to make

accurate thermocouple measurements;

22-bit or better A/D converter (DMM)

Does the Data Logger have internal

reference junction compensation?

Does the Data Logger have thermo-

couple conversion routines built-in?

Thermistors

• They measure absolute temperature

• A common thermistor type measures

5K at 25 C, with a 4% change per C

• Therefore, a 1 C change = 200 change

• 10 ohms of lead resistance would cause an insignificant 0.05 C error

Thermistor

• Often physically small mass • Won’t cause thermal loading • A large measurement current will cause self heating

Better accuracy than thermocouples, but more expensive

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Does the Data Logger have built-in

conversion routines for all the

common thermistor types?

R = V/I

Resistance Temperature Detector

(RTD)

• Avoid self heating - a 5 mA current source would create 2.5 mW of power in our RTD • At 1 mW/ºC, that is an error of 2.5/ºC

• Absolute temperature measurement

• Highly accurate measurement

• Platinum RTD has 100 at 0 C

with 0.385 / C

• 10 of lead resistance would cause

a 26 C error (very significant!)

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Does the Data Logger have built-in

conversion routines for the common

RTD types?

Integrated Circuit Temperature Sensor

Linear change in voltage or current with a change in temperature

• Absolute measurement

• 10 mV/K (voltage IC)

• 1 A/K (current IC)

• At room temperature, the output

is approximately 3V with a

10mV/°C change

• Limited temperature range < 150 C • Fairly large mass • Requires external power

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Temperature Sensor Summary

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Humidity Sensors Common humidity sensors include:

– Capacitive (RH)

– Resistive (RH)

– Thermal Conductivity (Absolute)

The sensor elements require circuitry for signal conversion, linearization, and

buffering. A separate bias supply is needed for power.

A capacitive sensor is well suited for measuring an environmental chamber’s humidity.

Its DC voltage output signal is in turn easily measured by the data acquisition

equipment’s DMM.

Do you need to measure Absolute Humidity or Relative Humidity?

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Strain Gage Measurements

Use a Wheatstone bridge to provide offset nulling, increased gain

and temperature drift compensation.

You can also use a four-wire ohm measurement.

See a YouTube video at AgilentTube; Search on

“Static and Dynamic Forces Overview”

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Pressure Sensors

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Rotational Speed Sensors

RPM Sensor

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Rotational Speed Sensors

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See a YouTube video at AgilentTube;

Search on “Measuring Rotational Speed, Revolutions Per Minute”

Variable Reluctance

Sensor

Hall Effect Sensor

Sensor Summary

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The Data Logger needs to be able to measure and convert all these different

signal levels to meaningful measurements like temperature, humidity, rpm, etc.

Using 4-20 mA current loops

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Use a 250Ω termination resistor:

20 mA = 5 volts = wide open

4 mA = 1 volt = fully closed

0 mA = 0 volts = open circuit

Dealing with noise

Types of noise:

1. Common mode noise, generated by ground loops

2. Normal mode noise, generated by electromagnetic fields

3. Electrostatic noise, generated by rotating equipment, etc.

Thermocouples are highly

susceptible to noise:

• Very low output voltage

• Very long physical runs

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Reducing Common Mode Noise

Eliminate Ground Loops

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Reducing Normal Mode Noise Minimize coupling, add filtering

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MEASUREMENT TIPS

• Reduce the field strength interfering with the measurement. It is better to run more wire and avoid the field.

• Minimize the size of the measurement loop. Use twisted-pair cabling; it’s like making a smaller receiving antenna.

• Run the measurement wires perpendicular to high-current wires.

• Reduce normal mode currents with a filter. • Use an integrating A/D. Normal mode noise is

typically the same frequency as the line frequency.

• Trade speed for reading rate with the integrating A/D. For 60 Hz line frequency,

60 readings per second can be achieved using 1 PLC; only 6 readings per second can be

achieved using 10 PLCs.

Reducing Electrostatic Noise Shielding is your friend

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Application Note, “Optimizing

Thermocouple Measurements in a

Noisy Environment”

http://cp.literature.agilent.com/litweb/

pdf/5990-9794EN.pdf

Converting Sensor Outputs to Useful Results

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Data Logger Instrument Requirements

Wide variety of signal types to measure

(Voltage, current, resistance, frequency, etc.)

Wide variety of signal levels to measure

(µV to 100V, µA to 3A, etc.)

Need to convert raw measurements into meaningful results

Need sufficient speed, accuracy and resolution

Should be easy to connect and re-configure sensors

Easy to set up, troubleshoot and program

Easy to transfer and analyze acquired data

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Data Logging Options

Pro

duct F

lexib

ility

High

Low

Just Enough

Performance:

Up to 60 channels,

3 slots, 8 modules

Higher Level

Performance:

Up to 560 channels,

8 slots, 21 cards

Balanced Throughput &

Performance:

High Density,

High Speed,

Many modules

34980A Multifunction Switch

Measure Unit

34970A/72A Data Logger

Price Performance Decision Criteria

M9000-series

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Agilent 34980A Multifunction Switch/Measure Unit

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• 8-slots, up to 560 2-wire channels

• Internal 6 ½ digit DMM

• Display to monitor setup and measured values

• Front panel for setup, control and debug

• Up to 1000 channels/second

• GPIB, USB, LAN (LXI)

• Remote access via built-in web interface

• Twenty-one plug-in modules

• Data Logger software included

34980A Demo System Slot 1: Dual 4x16 Armature MUX

Slot 2: 20-Ch 5A switch

Slot 3: N/C

Slot 4: 40-Ch MUX w/ thermocouples

Slot 5: Multi-function module

Slot 6: 4-Ch Isolated DAC

Slot 7: Quad 1x4 RF 50ΩMUX

Slot 8: N/C

“Okay, but how do I set it up and use it ??”

It’s Video Time !! Internal Web Server Demo

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Great, but how about programming and analysis??

Free BenchLink Data Logger Software

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34826A BenchLink Data Logger

High-speed data logging software with quick and easy access to measurements

Supports high-performance data logging

for 34980A Switch/Measure unit

Quick and easy test setup and execution

Collect, monitor and manage data

Set alarms and execute scans

Present data on a single channel or multiple channels

Export data to other applications for analysis

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34832A BenchLink Data Logger Pro

See Data Logger Pro videos at;

http://www.youtube.com/watch?v=EomiMQQivfY

http://www.youtube.com/watch?v=KPi9CUFB8zY

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?

? ?

Why is it so hard to get

the instrument

command sequence

into my programming

environment?

What are the

instrument

commands?

What is the correct

command syntax?

What are all of

the command

parameters?

Fine, but how about multiple instruments

and different programming languages?

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Command Expert combines

instrument command sets,

documentation, syntax

checking, command execution

and debugging all in one

interface.

Command Expert:

A new tool to help with instrument programming

Agilent Command Expert is a FREE software application that provides

fast and easy instrument control in many PC application environments

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Command Expert Key Capabilities

Assists in finding:

• Right instrument commands

• Setting the correct parameters

• Passing data and variables

Combines in one interface:

• Instrument commands

• Documentation

• Syntax checking

• Command execution

Integrates in:

• Excel®

• MATLAB

• LabVIEW

• Visual Studio®

• SystemVue

• VEE

Command Expert Overview - SCPI

Connect to instruments

Build, execute and debug sequences of commands

Search for commands

Perform commands

using correct

syntax and

parameters

View detailed command documentation

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It’s Video Time Again!!

Integrating into Excel

MATLAB integration

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Similar Experience in VEE and LabVIEW

E A S Y I N S T R U M E N T C O N T R O L N O W !

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www.agilent.com/find/commandexpert

For more information on Command

Expert…. Download the software at

www.agilent.com/find/commandexpert

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Reliable Measurement of Sensors/Transducers

We’ve talked about the following:

Selecting the correct sensors for your application

Reducing measurement errors due to noise and other factors

Identifying the necessary characteristics for your data logger system

Recognizing the benefits of an instrument’s built-in web server

and Data Logging Software

Seeing the benefits of Agilent’s Free Command Expert Software

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Questions ?

1. Find out more: www.agilent.com/find/34980temp

2. Watch the 34980A in Action on YouTube

3. Get a Quick Quote

4. Contact a Distribution partner

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Thank you for attending !!

Buy from an

Authorized Distributor

www.agilent.com/find/distributors

31 May 2012 11:00 AM MDT Focus on Switching: Multiplexers, Matrices and

System Performance

13 July 2012 11:00 AM MDT Focus on Control: Digital and Analog Control Tips

and Techniques

06 Sept 2012 11:00 AM MDT Focus on Data Acquisition: Setup, Programming,

Debugging and Maintaining a Reliable System