6. Measurements
6.1 Voltage measurements 46
6.2 Current-loop measurements 61
6.3 Resistance measurements 63
6.4 Thermocouple Measurements 69
6.5 Period-averaging measurements 70
6.6 Pulse measurements 71
6.7 Vibrating wire measurements 78
6.8 Sequential and pipeline processing modes 78
6.1 Voltage measurements
Voltage measurements are made using an ADC. A high-impedance programmable-gain
amplifier amplifies the signal. Internal multiplexers route individual terminals within the
amplifier. The CRBasic measurement instruction controls the ADC gain and configuration – either
single-ended or differential input. Information on the differences between single-ended and
differential measurements can be found here: Deciding between single-ended or differential
measurements (p. 48).
A voltage measurement proceeds as follows:
1. Set PGIAgain for the voltage range selected with the CRBasic measurement
instruction
parameter Range. Set the ADC for the first notch frequency selected with
fN1.
2. If used, turn on excitation to the level selected with ExmV.
3. Multiplex selected terminals (SEChan or DiffChan).
4. Delay for the entered settling time (SettlingTime).
5. Perform the analogue-to-digital conversion.
6. Repeat for input reversal as determined by parameters RevEx and RevDiff.
7. Apply multiplier (Mult) and offset (Offset) to measured result.
Conceptually, analogue voltage sensors output two signals: high and low. For example, a
sensor that outputs 1000 mV on the high signal and 0 mV on the low has an overall output of
1000 mV. A sensor that outputs 2000 mV on the high signal and 1000 mV on the low also has an
overall output of 1000 mV. Sometimes, the low signal is simply sensor ground (0 mV). A single-
ended
6. Measurements 46
To Next Page
Loading...
