2
1.3 General Description
(continued)
The transmitter is normally powered by an unregulated power supply as
shown in
Figure 1-1
. The proportionally-transmitted signal begins at 4mA,
at the low end of its temperature range, and increases to 20mA, at the
high end of its temperature range. (There are various temperature ranges/
thermocouple types available for the transmitter. To order, refer to
Section
1.5
for correct Model Numbers and Range Codes.)
Figure 1-1 Thermocouple Transmitter
The two-wire transmitter receives and measures signals from
themocouples and sends an output current of 4-20mA which is directly
proportional to the thermocouple millivolt input. It is designed to connect
with only two copper wire leads that will supply the voltage to operate the
transmitter from a power supply, and also carry the output current. The
output current is used for recording, computing, or controlling.
If the transmitter is mounted inside a protection head, (see
Figure 2-1
), the
thermocouple extension wires are replaced by two copper wires that carry
the 4-20mA signal and dc voltage to operate the transmitter.
The transmitter has reverse supply polarity protection and will operate with
a wide range of supply voltages (8 to 35 Vdc). It has an input sensor break
protection circuit that forces the output current to go upscale when the
thermocouple wire opens.
The transmitter does NOT provide isolation between its input and the
4-20 mA output; therefore, an ungrounded thermocouple junction is
suggested to prevent possible ground loops.
