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
:
