Measurement Computing Data Acquisition Systems rev.10.4 - Manual (Page 173)

Reading Scan
Shorted Channels 0 1 2 3
1 V (ignored) V (ignored) CJC J1a J1b J1c
2 V (ignored) V (ignored) CJC J2a J2b J2c
3 V (ignored) V (ignored) CJC J3a J3b J3c
4 V (ignored) V (ignored) CJC J4a J4b J4c
In either case, the CJC and T/C readings are used to produce one temperature result for each T/C reading.
Thus, the 24 original readings are reduced to 12 temperatures.
To measure temperatures, the scan must be set up so the T/C measurements consecutively follow their
corresponding CJC measurement (the CJC measurement need not be the first element in the scan). If auto-
zeroing is enabled, the CJC measurement must be preceded by both a CJC zero measurement and a T/C zero
measurement.
All of the thermocouples converted with a single invocation of the conversion functions must be of the same
type: J, K, T, E, N28, N14, S, R, or B. To measure with more than one type of thermocouple, they must be
sorted by type within the scan, and each type must be preceded by the related CJC.
The scan is not restricted to thermocouple measurements. The scan may include other types of signals such as
voltage, current, or digital input; but conversion of these readings cannot be performed by the temperature
conversion functions cannot handle them.
T/C Gains Settings
The temperature measurements must be made with the correct gain settings. The gain settings for the different
thermocouple types depend on the bipolar/unipolar setting of the device, and the type of card being used. PC
cards can only be set for bipolar acquisitions, and have their own set of gain codes. The gains settings should
be established with the daqAdcSetScan function, as specified in the following tables.
Unipolar operations are not recommended for thermocouple measurement unless the
measured temperatures will be greater than the device temperature.
DBK19 and DBK52 Gain Codes
T/C
Type
Unipolar Gain Code Bipolar Gain Code Bipolar Gain Codes for
Daq/2000 Series devices*
and PC Cards
CJC Dbk19UniCJC Dbk19BiCJC Dbk19PCCBiCJC
J Dbk19UniTypeJ Dbk19BiTypeJ Dbk19PCCBiTypeJ
K Dbk19UniTypeK Dbk19BiTypeK Dbk19PCCBiTypeK
T Dbk19UniTypeT Dbk19BiTypeT Dbk19PCCBiTypeT
E Dbk19UniTypeE Dbk19BiTypeE Dbk19PCCBiTypeE
N28 Dbk19UniTypeN28 Dbk19BiTypeN28 Dbk19PCCBiTypeN28
N14 Dbk19UniTypeN14 Dbk19BiTypeN14 Dbk19PCCBiTypeN14
S Dbk19UniTypeS Dbk19BiTypeS Dbk19PCCBiTypeS
R Dbk19UniTypeR Dbk19BiTypeR Dbk19PCCBiTypeR
B Dbk19UniTypeB Dbk19BiTypeB Dbk19PCCBiTypeB
* Daq/2000 Series devices include DaqBook/2000 Series, DaqScan/2000 Series, DaqLab/2000 Series, and
DaqBoard/2000 Series devices.
Programmer’s Manual 908494 Daq API Command Reference 4.3-47