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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
Voltage = Current X Resistance
(E=IR)
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Some Rules Help
Current is constant throughout circuit
Voltages are different at points 1,2,3,4
Current can vary through R1,R2,R3
Voltage is similar at Points 1,2,3,4
Voltage is similar at points 8,7,6,5
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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
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Jumpers on ESC Met Card
Close tolerance resistors
Jumpers
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Met One 083D to ESC Met Card
18.7 k
Temp Probe
23.1 k
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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?
5 Volts
+50°C
Full range of sensor
Multiplier
=
Full range of voltage
2.5 Volts
100°C
0°C
Voltage
-50°C
Temperature
20
5 Volts
100°C
0 Volts
=
5000 Millivolts
=
0.02
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°C
range would be
180 °F
(-50°C = -58 °F)
(+50 °C = +122
°F)
(122 + 58 = 180)
Depending on whether the datalogger uses volts
or millivolts the multiplier will be either 20 or 0.02
What is the offset?
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Offset examples
Where is the low end of the instrument range in relation to 0?
0
+50 ºC
-50 ºC
Temperature ºC
+122 ºF
-58 ºF
Temperature ºF
Range = 100 ºC
Low end of range = -50
Offset = -50
Range = 180 ºF
Low end of range = -58
Offset = -58
223 K
323 K
Temperature in Kelvin
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Offset is +223
0
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
ESC
Where is the
wire connected?
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Analog Examples
Campbell
Multiplier
PPB Range 500
Volts 5000 mV
500
= 0.1
5000
Volt range
Where is the
wire connected?
UNITS !!!
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Note that SE 1 and 2 and DIFF 1 are the same screws
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Zeno
Where it is wired
Multiplier
Offset
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Note that Ch1 has a “–” and a “+”
A differential connection on Ch1 would just say 1
A single ended connection would say “1-”, or “1+”
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Single-Ended & Differential Voltage
(Campbell Scientific – SE & DIFF)
Sensor
Sensor
2.5 Volts
(H)
2.5 Volts
2.5 Volts
Datalogger
.1 Volt
(L)
2.4 Volts
Datalogger
Single-Ended
measures between
SE terminal and ground
SE
Ground
Differential
measures between
two voltages
2
1
(Single-ended channel 2)
1
Diff
(Differential Channel 1)
H
L
(Screw-on datalogger)
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Foil and ground
wire for shielding
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Alternating current sine wave
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Wind Speed Sensors
• Wind Speed
Hz (Hertz) is cycles per second
Sine wave
Use sensor unit specs for range
+
-
Pulsed frequency
Also, varying voltage, for example
0 volts = 0 mph
5 volts = 112 mph
+
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Time
Wind Speed examples
ESC
Campbell
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EPA’s Technology Transfer Network
http://www.epa.gov/ttn/
http://www.epa.gov/ttn/amtic/qalist.html
Some videos
What about wind direction averaging?
North
Winds 2:00pm to 2:30pm
Met site
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!
South
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?
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.
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
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
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Wind direction
must be
properly aligned
to north, usually
true north
Magnetic
declination is the
difference
between magnetic
and true north
True
North
Magnetic
North
South mark
on sensor
Declination calculator
http://www.ngdc.noaa.gov/geomagmodels/Declination.j
sp
Graphic from USGS
Rain
ESC
Campbell
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As a side note, what is warmup all about and how does that relate to power out?
Sensor grounds
Power grounds & Power outs
Or can use a ground terminal
for power grounds
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Datalogger Power
• 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
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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
Compatibility (cont.)
• 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
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Internet
Or
Intranet
Local Network
ESC 8832 Ethernet connection
Must set IP addresses
Router
ESC cable
Computer cable (laptop, for example)
ESC 8832 Ethernet connection
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
Inst. 1
Rx
Inst. 2
Rx
Null Modems
If you notice
both serial
connections
are male
pins
Inst. 1
Tx
Wires
Tx
You may
need a null
modem
adapter or
cable
Inst. 2
Rx
Wires
Tx
Won’t work
Rx
Tx
Will work
A gender
changer
doesn’t
change the wire
orientation. It is
a “straight
through”
connection to
In general, although
individual adapters can adapt male and
female pins
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.
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HyperTerminal
From ESC 8832 manual:
(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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To computer, LAN,
Internet, etc.
Router
Serial to
Ethernet
adapter
Notice
null
modem
Office
Radio
Site
Datalogger
2 antennas
Site
Radio
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!
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