Measurements; Voltage Measurements - Campbell CR300 Series Product Manual

18. Measurements

18.1 Voltage measurements

18.2 Current-loop measurements
18.3 Resistance measurements
18.4 Period-averaging measurements
18.5 Pulse measurements
18.6 Vibrating wire measurements
18.1 Voltage measurements
Voltage measurements are made using an Analog-to-Digital Converter (ADC). A high-
impedance Programmable-Gain Amplifier (PGA) 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:
single-ended or differential
A voltage measurement proceeds as follows:
1. Set PGA gain 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, such as with bridge measurements, 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 analog-to-digital conversion.
6. Repeat for input reversal as determined by parameter RevDiff.
7. Apply multiplier (Mult) and offset (Offset) to measured result.
Conceptually, analog 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
measurements (p. 189).
90
92
95
101
102
107
Deciding between
18. Measurements 90