Campbell CDM-A100 Series, Instruction Manual

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CDM-A100 Series
14
6.2 Resistance Measurements – Specifications
Resistance measurements for four- and six-wire full-bridge and two-, three-,
and four-wire half-bridge using voltage excitation or direct resistance
measurements using current excitation. Excitation polarity reversal minimizes
DC error.
Terminals
CDM-A108: SE terminals 1-16
DIFF terminals 1H/1L – 8H/8L
Excitation terminals X1 – X2
CDM-A116: SE terminals 1-32
DIFF terminals 1H/1L – 16H/16L
Excitation terminals X1 – X4
Accuracy
1,2
0 to 40 °C: ±(0.02% of voltage measu offset)
–40 to 70 °C: ±(0.025% of voltage measu offset)
–55 to 85 °C: ±(0.03% of voltage measu offset)
1
Assumes input reversal for differential measurements and excitation reversal for
excitation voltage <1000 mV and excitation current <1 mA, not including bridge
resistor errors and sensor and measurement noise.
2
See CR6 Datalogger Manual for help estimating measurement accuracy for ratiometric
measurements. For Resistance() instruction, the excitation current is internally
measured across an internal resistor (200
Ω, ±
0.005% @ 25 °C, 2 ppm/°C TCR) with
sensor resistance determined as Vs/Ix, where Ix is the measured excitation current and
Vs is the returned sensor signal.
6.3 Voltage and Current Excitation – Specifications
Two terminals on the CDM-A108 and four terminals on the CDM-A116 can be
configured for voltage or current excitation using a 12-bit D-to-A converter.
When used for ratiometric-resistance measurement, excitation is active only
during measurement.
Terminals
CDM-A108: X1 – X2
CDM-A116: X1 – X4
Voltage Excitation
Range: ±5000 mV
Accurracy
1
0 to 40 °C: ±(0.05% of s 2.5 mV)
–40 to 70 °C: ±(0.08% of s 2.5 mV)
–55 to 85 °C: ±(0.1% of s 2.5 mV)
Resolution: 1.25 mV
Maximum Source or
Sink Current: ±50 mA