Connection To A Data Logger; Tvb1 And Tvb-M Tensiometer Power Supplies - Delta-T Devices SWT5 User Manual

In a full-bridge the signal must be measured differentially. This means
do not measure only signal plus against common ground, but measure
the voltage drop between signal minus against common ground and
signal plus against common ground.
The supply voltage has to be constant and stabilized.
The supply voltage must not exceed 18 VDC.
If the Tensiometer is not permanently powered the warm-up before
a measurement should be no greater than 10 seconds. The 99%
value is reached in 0.01 seconds, so a 1 s warm up is fine.
If the Tensiometer is supplied with 10.6 VDC the output signal range
is around 5.3 VDC. A data logger must have the capability to
measure such a signal level, but many loggers cannot do this.
In such cases use a TV batt (type TVB1 or TVB-M) power supply.

3.4.4 Connection to a data logger

The pressure transducer is a non-amplified bridge circuit which is
calibrated for 10.6 VDC and requires a stabilized power supply.
Some logger types can measure bridge circuits directly, other loggers
require certain measures as the signal minus and the supply minus do
not have the same ground.
When supplied with just 10.6 V (supply minus = 0 V and supply plus =
10.6 V) the output signal range is between +3.2 V (min.) and +6.8 V
(max.) related to power supply minus.
Other supply voltages are possible, but the output signal range has to
be recalculated.

3.4.5 TVB1 and TVB-M Tensiometer power supplies

These power supplies are designed for Tensiometers SWT3, SWT4,
SWT4R and SWT5. They offers a stabilized 10,6 V power supply,
supplying -5 V and +5,6 V for powering up to 30 tensiometers.
These provide tensiometer output signals of <1V, which is suitable for
many loggers,
The TVB1 fits inside a DL2e logger terminal compartment.
The TVB-M module has no environmental protection and can fit into
an M-ENCL enclosure, and requires 7.5 – 16.0 V DC.
20  Installation
SWT5 User Manual v2