Measurement Computing Personal Daq/3000 Series - Manual (Page 80)

A-2 Signal Modes and System Noise 937492 Appendix A
Connecting Thermocouples to Screw Terminal Blocks
Personal Daq/3000 Series modules can measure 16 channels of voltage in single-ended mode, 8 channels
of voltage in differential mode, or 8 channels of temperature in differential mode. You can, of course, mix
signal types, for example have some channels connected to thermocouples and others connected to
voltage signals.
Thermocouple wires are to be connected
in differential mode only.
Differential connection is made as follows:
(a)
the red thermocouple wire
connects to the channel’s
Low (L) connector.
(b)
the other color wire
connects to the channel’s
High (H) connector.
Personal Daq/3000 Series and PDQ30 devices do not have open thermocouple detection.
Single-Ended (V1 and V2) and Differential (V3) Connections to Analog Input Channels
Thermocouple wire is standardized, color-coded, and polarized, as noted in the following table.
Thermocouple Standards
T/C
Type
(+) Lead to
Channel High
(-) Lead to
Channel Low
J White Red
K Yellow Red
T Blue Red
E Violet Red
N28 Orange Red
N14 Orange Red
S Black Red
R Black Red
B Gray Red
Thermocouples output very small voltages and long thermocouple leads can pickup a large amount of
noise. If desired, noise reduction can be achieved through the use of shielded thermocouples and/or
averaging.
You can minimize the effect of noise by employing one or more of the following practices.
Using all three is best.
(1) Use shielded thermocouples (see Shielding, page A-3)
(2) Average readings (see Averaging, page A-5)
(3) Route thermocouple wires away from others. Wires adjacent or close to TC
wires may introduce noise into the TC wires. For example, you should never route TC
wires in a conduit that is being used for mains or motor drive power. Such practices
could introduce a great deal of signal noise.