Indirect Measurements; Measurements From Other Modules - National Instruments SCXI-1121 User Manual

Programming
gains of both the SCXI-1121 and the data acquisition board when calculating the actual voltage
present at the input of the SCXI-1121.
To measure one of the four differential input channels to the SCXI-1121, perform the following
steps:
1. Write the binary pattern 000XXXCC XX000000 to the SCXI-1121 Configuration Register.
2. Measure the voltage with the data acquisition board.
To shunt calibrate one of the four differential input channels, perform the following steps:
1. Write the binary pattern 001XXXCC XX00000 to the SCXI-1121 Configuration Register.
Insert a delay of at least 1 sec if you have set the 4 Hz filter, or at least 1 msec if you have set
the 10 kHz filter. This delay permits the SCXI-1121 amplifier to settle.
2. Measure the voltage with the data acquisition board.
To measure the voltage on the MTEMP line, perform the following steps:
1. Write the binary pattern 000XXXXX XX100000 to the SCXI-1121 Configuration Register.
2. Measure the voltage with the data acquisition board.

Indirect Measurements

Indirect measurements involve one module sending a signal to Analog Bus 0, where it is picked
up by another module and transmitted to the data acquisition board.

Measurements from Other Modules

To perform measurements from other modules, you must cable the SCXI-1121 rear signal
connector to a data acquisition board. See Chapter 2, Configuration and Installation, for more
information. To make a measurement from another module, perform the following steps:
1. Perform any necessary programming to ensure that no modules are driving Analog Bus 0.
For an SCXI-1121, clearing AB0EN in the Configuration Register will ensure that its output
is not driving AB0.
2. Write the binary pattern 000XXXXX XX100011 to the SCXI-1121 Configuration Register.
This step disables the SCXI-1121 from driving Analog Bus 0 and allows Analog Bus 0 to
drive MCH0 through the output buffer.
3. Program the other module to drive Analog Bus 0 with the signal to be measured.
4. Measure the voltage with the data acquisition board.
SCXI-1121 User Manual 5-4 © National Instruments Corporation
Chapter 5