Datalogger Considerations

Presented by: Glenn Gehring

Technology Specialist III

Institute for Tribal Environmental Professionals (ITEP)

Tribal Air Monitoring Support (TAMS) Center

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Dataloggers and Met

• An overview—not comprehensive

• Focused on the practical

• Detailed training is available from datalogger manufacturers

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Common Types of Communication• Analog

• Instrument outputs a voltage• Datalogger senses voltage• Both must know what the voltage represents

• Range of voltage used concentration range of instrument must be coordinated between datalogger and instrument

• Digital• Direct communication – data streams

• Compatibility and connection/communication parameters

• Current• Instrument outputs current• Current is passed through a close-tolerance resistor• Datalogger senses voltage drop across resistor

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Electricity

• Voltage is electrical potential• Provides driving force for current flow

• Current• Movement of electrons through a conductor

• Resistance• resistance to current flow

• OHM’s Law – there is a relationship

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Voltage = Current X Resistance (E=IR)

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Some Rules Help

Current is constant throughout circuitVoltages are different at points 1,2,3,4

Current can vary through R1,R2,R3Voltage is similar at Points 1,2,3,4Voltage is similar at points 8,7,6,5

See www.allaboutcircuits.com to learn more about basic circuits

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• Some sensor manufactures provide jumpers on their units so you can change outputs.

• Example: some RM Young wind speed sensors can be set to either a 1- or 5-volt output by moving jumpers on the sensor

Jumpers on ESC Met Card

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Jumpers

Close tolerance resistors

Met One 083D to ESC Met Card

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23.1 k

Temp Probe

18.7 k

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Voltage Temperature Depending on whether the datalogger uses volts or millivolts the multiplier will be either 20 or 0.02

What is the offset?

-50°C

Example of analog datalogger concepts: let’s look at configuring an analog temperature sensor to a datalogger. We will determine the multiplier and the offset to enter into the datalogger.

Assume the temperature sensor senses a range of temperatures from -50°C to +50°C. That means the sensor can measure a total range of 100°C. Also, let’s assume the sensor has a 5-volt maximum

output. What is the multiplier and what is the offset?

+50°C

0 Volts

5 VoltsFull range of sensor

Full range of voltage= Multiplier

=100°C

5 Volts20

=100°C

5000 Millivolts0.02

Note: If I wanted to also log °F or Kelvin I could create additional channels and use unit conversions to get multipliers. In this example, the 100°Crange would be 180 °F (-50°C = -58 °F) (+50 °C = +122 °F)(122 + 58 = 180)

2.5 Volts 0°C

Offset examplesWhere is the low end of the instrument range in relation to 0?

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0

0

Temperature ºC

-50 ºC +50 ºC Range = 100 ºCLow end of range = -50

Offset = -50

223 K 323 K

Temperature ºF

-58 ºF +122 ºF Range = 180 ºFLow end of range = -58

Offset = -58

Temperature in Kelvin

Offset is +223

Datalogger Configuration Differences• Some dataloggers need a multiplier and an

offset for configuration• ESC asks for

• Volts High Input• Volts Low Input• High Output E.U.s• Low Output E.U.s

And then calculates multiplier and offset

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Analog Examples

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ESC

Where is the wire connected?

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Analog ExamplesCampbell

Where is the wire connected?

Volt rangePPB Range 500Volts 5000 mV

500

5000= 0.1

UNITS !!!

Multiplier

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Note that SE 1 and 2 and DIFF 1 are the same screws

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Where it is wired

Offset

Multiplier

Zeno

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Note that Ch1 has a “–” and a “+”A differential connection on Ch1 would just say 1A single ended connection would say “1-”, or “1+”

Single-Ended & Differential Voltage(Campbell Scientific – SE & DIFF)

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2.5 VoltsDatalogger

2.4 VoltsDatalogger

Ground

.1 Volt(L)

2.5 Volts(H)

Differentialmeasures between

two voltages

2.5 Volts

Single-Endedmeasures between

SE terminal and ground

Sensor Sensor

1

H L

Diff

SE 1 2

(Differential Channel 1)

(Screw-on datalogger)

(Single-ended channel 2)

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Foil and ground wire for shielding

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Alternating current sine wave

Wind Speed Sensors• Wind Speed

Sine wave

Pulsed frequency

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Time

+

+

-

Hz (Hertz) is cycles per second

Use sensor unit specs for range

Also, varying voltage, for example0 volts = 0 mph

5 volts = 112 mph

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Wind Speed examples

ESC

Campbell

http://www.epa.gov/ttn/amtic/qalist.html

EPA’s Technology Transfer Networkhttp://www.epa.gov/ttn/

Some videos

What about wind direction averaging?

Met site

North

South

Winds 2:00pm to 2:30pm

Winds 2:30pm to 3:00pm(slower wind speed)

Consider this. The datalogger is typically set to average winds every hour. If winds blow from the north for ½ hour and then

shift to the south for the next ½ hour, what is the 1-hour average direction the

winds came from during that hour?

(0 degrees + 180 degrees) ÷ 2 = 90 degrees(scalar averaging)

But, the winds never blew from the east!

Looking at the wind speed differences we intuitively see that the net impact on the

movement of pollutants would be movement toward the south since the

wind speeds were higher from the north.Vector averaging looks at both wind

speed and direction.

As if that isn’t enough, 360 and 0 degrees represent the same thing.

And, what do we do when averaging during an hour that has both calm

winds and winds? Also, what about vertical movement?

More about Wind-Direction Averaging• Some dataloggers have math packs that configure several

channels for wind automatically. You can use both scalar and vector averaging at same time from same wind sensors

• Some dataloggers have ability for more complex programming to suite your specific needs (you must understand basic computer programming to do this, but some dataloggers allow for a high degree of customization)

• So how do we interpret winds from our sensors? That can be complex.

• In simple terms when you see a vector average you are looking at both wind speed and wind direction combined into vectors. The 1-hour averaging provides the net result (resultant) on air movement for the hour

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Wind-Direction Averaging (cont.)

• Sometimes winds are mostly from one direction during the hour. Sometimes they vary a lot

• Sigma Theta (term used in hourly data): standard deviation of winds during hour

• “High sigma theta” means highly variable winds where “low sigma theta” indicates winds are more consistent

• Important when interpreting wind data• Sometimes it is good to know maximum gust each

hour in addition to hourly average.• I recommended you configure datalogger to log

maximum gusts

Declination calculatorhttp://www.ngdc.noaa.gov/geomagmodels/Declination.jsp

TrueNorth Magnetic

NorthMagnetic

declination is the difference

between magnetic and true north

Wind direction must be

properly aligned to north, usually

true north

South mark on sensor

Graphic from USGS

Rain

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ESC

Campbell

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Sensor grounds

Power grounds & Power outs

Or can use a ground terminal for power grounds

As a side note, what is warmup all about and how does that relate to power out?

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• Option to add heaters on some sensors (eg. wind sensor)

• Used so ice/snow won’t stop measurements • Or, in case of precipitation gauge, to melt snow/ice

for total precipitation measurements • You can NOT power heater with power from datalogger

• Power supplies limited • You can typically power sensor from datalogger, or from

separate power supply • But heater wires must use separate power supply

capable of supplying electrical demands of heater

Datalogger Power

Compatibility!!!

• Meteorological sensors have variety of output signals datalogger must interpret and log

• Wind speed sensors can output signals as varying voltage, an alternating current, direct current pulse, etc.

• Datalogger must have capability to accept this type of signal at range of frequencies your wind speed sensor outputs.

• Not all dataloggers can accept frequency signals or have limited frequency ranges they can accept.

• A tipping bucket rain gauge outputs a signal when enough rain has entered to cause it to tip

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• Datalogger must count number of tips in a period of time. Sensors with analog outputs (voltage outputs) have ranges such as 0 - 1 volt, 0 - 5 volts, or higher

• Sometimes analog output signal depends on voltage you supply to sensor

• If datalogger can only accept 2500 millivolts (2.5 volts), 0 - 5 volt sensor would be more difficult to connect

• Put on your electrical engineer hat & it can be done, but do you own an electrical engineer hat? Why make it hard? Think it through and triple check everything for compatibility with different sources before you purchase

Compatibility (cont.)

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InternetOr

IntranetLocal Network

Router

ESC 8832 Ethernet connection

ESC cable

Computer cable (laptop, for example)

ESC 8832 Ethernet connectionMust set IP addresses

Do I need a crossover cable to connect???- not likely when connecting through a router.

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USB to serial adapter connects to computer. Or you may have a serial port on the

computer

If you notice both serial

connections are male

pinsA gender

changer doesn’t change the wire orientation. It is

a “straight through”

connection to adapt male and

female pinsIn general, although

individual adapters can be different, the null modem switches the receive and transmit wires on the cable. If one instrument sends

on a wire the other must be able to receive on that same wire. If they

both try to send or receive on the same

wire it won’t work.

You may need a null

modem adapter or

cable

Rx

Tx Tx

RxInst. 1 Inst. 2

Won’t work

Tx

Rx Tx

RxInst. 1 Inst. 2

Will work

Wires Wires

Null Modems

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From ESC 8832 manual:

HyperTerminal

(XP, or XP Mode in Windows 7, built in terminal communications software)

For serial communications these settings MUST match

your datalogger

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SiteDatalogger

Serial to Ethernet adapter

Notice null

modem

Office Radio

2 antennas

Site Radio

Router

To computer, LAN, Internet, etc.

Basic telemetry (one of many methods)

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In truth, dataloggers could be an entire course! Oh yeah, it IS! It just hasn’t been offered in a while. This course touches on dataloggers, but I’m still learning and I imagine I will still

be learning a decade from now. That’s the fun and that’s the challenge. Each of us needs to develop our own

understanding. We each need to trudge through until we get a working knowledge, and then if we are of the curious sort, we keep trying to improve our understanding. The exercises in this course are designed to introduce concepts rather than just focusing on procedures. If you understand the system,

the concepts, you can do anything. A step-by-step procedure only teaches a procedure. We do have procedures built in,

but hopefully you can take some time to explore the equipment. How does it work? Why am I doing this

procedure? Where IS that coffee pot? Happy learning!