
Other bridge sensors
Sensor connection
Connect sensor wires to GP1-PBA1 terminals:
GND, Vref Precision bridge excitation or power supply
CH(-), CH(+) Bridge output
Step2: Measure the zero offset
If possible, zero the sensor output and connect the sensor to the GP1-PBA1, otherwise
fit the Calibration Resistors and wire link, as for SWT5 tensiometers.
Measure the zero offset,as for SWT tensiometers.
Step 3: Program the GP1 for bridge sensor readings
Proceed as for SWT tensiometers.
In Voltage Channel Properties, enter appropriate Warmup, Units, Minimum,
Maximum and Resolution values for your sensor.
To record sensor readings in mV: enter a1 = 0.02 [the GP1-PBA1 gain is 50]
For readings in ‘engineering units’, calculate a1 from sensitivity and excitation voltage
values provided by the manufacturer of the sensor.
Sensitivity is typically specified as mV per engineering unit, at a given excitation
voltage in volts, e.g. 0.1mV / hPa at 10.6V excitation:
a1 = excitation voltage / ( 150 x sensitivity ) [3 volts, times a gain of 50]
Alternatively, sensitivity may be specified in mV per engineering unit per volt excitation,
e.g. 0.01mV per mbar per volt excitation:
a1 = 1/ ( 150 x sensitivity )
In all cases, calculate and enter a0 = – a1 x zero offset
Specification
Typical contribution to reading errors after zero offset correction, assuming nominal excitation and
gain values
Electrical parameters
Precision bridge excitation: 3.0V
Bridge impedance: >300 Ώ
Input range: ±29 mV
Gain: 50
Output offset: 1250 mV nominal
Accuracy
0 to 40°C: ±0.1 mV ±0.06% of reading
-20 to +60°C: ±0.2 mV ±0.08% of reading
SWT tensiometer (0 to 40°C): ±4 hPa ±0.06% of reading
Other bridge sensors: If common mode changes after
zero offset measurement add ±0.14 mV / V of CM change
Notices
All parts of the GP1 Data Logger and GP1-PBA1 Precision Bridge Adapter designs and
documentation are the exclusive property of DeltaT Devices Limited, and are covered under
international copyright law.
Delta-T Devices Ltd
128 Low Road, Burwell
Cambridge CB5 0EJ
UK
Tel: +44 1638 742922
Fax: +44 1638 743155
web: www.delta-t.co.uk