VTI Instruments Ametek EX1200A Series, User Manual

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EX1200A Triggering 103
If the thermistors are connected to a multiplexer card, the wiring is similar to that of a 2-wire
voltage measurement without the polarity constraints, as the thermistors are bilateral passive
devices.
DMM Backplane
B
P
L
_
H
I
B
P
L
_
L
O
B
P
L
_
S
H
I
B
P
L
_
S
L
O
CH 1
CH 2
CH n
Thermsitors
EX1200
Multiplexer Cards
EX1200 Mainframe
F
IGURE
4-21: T
HERMISTOR
C
ONNECTIONS VIA
DMM B
US
Programming Interface
The VTEX DMM and VTEX Scanner drivers provide the access to the features of EX1200A
DMM. Refer to the below functions of the driver in its documentation.
IVTEXDmmTemperature Interface
IIviDmmTemperature..::.Thermistor Property
Scanlist Application Note
When using scanlist with temperature measurements, it is important not to make any configuration
modification between running the scan list and reading the data. For example, using the following
sequence would result in an erroneous reading:
1) Set up config
“
CJC
”
with 10k thermistor
Run scanlist
Change
“
CJC
”
to use 5k thermistor instead
Read back data
The EX1200A performs the needed temperature calculation based on the current settings. As a
result, the data taken with the 10k thermistor would have 5k-related math applied, resulting in
incorrect data. In the same respect, if the temperature configurations are deleted after the scan list
is run and the user attempts to read the data, an “Bad Configuration Index” error will occur. This is
the result of the EX1200A attempting to perform calculations without configuration data.