8
Connection assignment
1 + RH
2 wire techn. 4 to 20 mA = 0 to 100 %RH,
2 - RH
2 wire techn. 4 to 20mA
= -20 to +70 °C
(with WHT -20/70 / DHT -20/70 / PHT -20/70)
2 wire technology 4 to 20 mA = -20 to +120°C
(with DHT -20/120 / PHT -20/120)
4 - °C
3+°C
In order to avoid losing the adjustment values,
adjustment buttons should only be activated if the
adjustment container is screwed on (see page 10,
adjustment with control and adjustment set).
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2 wire transmitters are used to convert non-electrical
parameters, e.g. temperature, pressure,
relative humidity etc. to an electrical standard signal of 4
to 20 mA.
The transmitters are connected to a d.c. voltage source
by means of 2 cables. The power consumption of the
transmitter from the d.c. current source changes linearly
in the range from 4 to 20 mA, depending on the
parameter being measured.
The advantages of the two wire system are easy
installment and problem-free connection. The length of
the cables does not influence the measured signal. A
further additional advantage is the so-called “live zero”
signal i.e. 0 parameter corresponds to a current of 4
mA. In this way, this value is also clearly transmitted and
cannot be confused, for example, with a system which
is switched off or an ununterrupted line.
Description of 2 wire technology
Connection socket
for scaling adapter
or testo 400/650
instrument for
1-point adjustment
1 2 3 4
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