Measurement Computing CIO-EXP-RTD16 - Manual (Page 16)

5 RTD MEASUREMENT CONFIGURATION
An RTD is a temperature sensor that consist of a resistive element, usually a length of wire encased in a
sheath. Various wire materials are used with platinum being the most common. There are three types of
hookups: two-wire, three-wire, and four-wire. An excellent source of information on RTDs and how to
select one for your application may be found in the OMEGA Engineering catalog.
5.1 CHANNEL SELECTION
The General Configuration section describes the channel selection, setting the jumper and verifying the
installation and operation of the CIO-EXP-RTD16 with your data acquisition board. Configure your
boards as described in that section before continuing with this section.
5.2 POWER SOURCE SWITCH
The General Configuration section describes the power selection options, setting the power select switch
and verifying the installation and operation of the CIO-EXP-RTD16 with your data acquisition board.
Configure your boards as described in that section before continuing with this section.
5.3 DETERMINING THE APPROPRIATE GAIN
To select the best gain for RTD type, base resistance and temperature range, consider that RTD
resistance changes with temperature, but the magnitude of the change also changes with temperature.
RTD type determines the ‘slope’ of the ohms vs. temperature curve. The most popular type has an
‘alpha’ of .00385, known as the European standard. Its value is .00385 ohms per ohm per °C.
The Universal Library and InstaCal support six different RTD types. Please call if you do not see the
RTD you are interested in listed here.
Material ‘alpha’
Platinum 0.00392 American standard
Platinum 0.00391
Platinum 0.00385 European standard (Most popular, OMEGA’s standard also)
Copper 0.00427
Nickel/Iron 0.00581
Nickel/Iron 0.00527
To determine which gain to use, you must know the maximum temperature the RTD will be used to
measure, and thus the maximum change in resistance that the RTD will undergo. Here is a table for
platinum:
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