SWT4 User Manual v3.1
Installation
23
3.5 Connecting SWT4 and SWT4R
3.5.1 Spot reading with the SWT-MR
(Infield7)
SWT4
and
SWT4R
are fitted with a 4-pin plug. The plug can be
connected directly to an
SWT-MR
handheld measuring device for
taking spot readings of the soil water tension. This displays and stores
the soil water tension.
3.5.2 Connecting cables
Connecting and extension cables are required for connecting
SWT4
and
SWT4R
to a data logger or other data acquisition device.
Find cables in the chapter “Accessories” on page 43.
3.5.3 Connection to a data logger
Delta-T Logger users: see
24.
The pressure transducer is a non-amplified full Wheatstone bridge
circuit which is calibrated at 10.6 VDC. It requires a stabilized power
supply.
Some logger types can measure bridge circuits directly, other loggers
require additional measures, because the signal minus and the supply
minus do not have the same ground.
If supplied with exactly 10.6 V (i.e. supply minus = 0 V and supply plus
= 10.6 V) the Tensiometer output signal range is b3.2 V (min.)
and +6.8 V (max.) relative to the power supply minus.
This may be outside the common mode range of some loggers.
Other supply voltage ranges are permissable, but the output signal
range has to be recalculated.
The supply voltage must be constant and stabilized.
If the Tensiometer is not permanently powered, the warm-up period
before a measurement is normally 1 second. It should be no greater
than 10 seconds.
The Tensiometer plug should be covered with the protective cover
(as supplied) when not connected to a cable.
The supply voltage must not exceed 18 VDC.
