SEM104TC Datasheet, PDF (3/8 Pages) List of Unclassifed Manufacturers – SEM104 SERIES

Figure 1
ZS
+
-
Ø 42.0 mm
23.0 mm
Mounting holes : 2 holes 5.5 mm diameter, 33 mm centres
Centre hole sensor wire entry : 4.0 mm diameter
Figure 2
Page 3
3.2 ELECTRICAL
Connections to the transmitter are made to the screw terminals provided on the top face. To maintain CE
compliance, input wires must be less than 3 m in length and output wiring must be screened cable, with
the screen earthed at one end only. All three input wires must have the same core diameter to maintain
equal lead resistance in each wire. A hole is provided through the centre of the transmitter to allow
sensor wires, (entering direct from the probe assembly via a base entry), to be threaded through the
transmitter body, direct to the input screw terminals. The screw terminals have been designed to allow all
connection wires to enter from either an inner or outer direction.
The transmitter is protected against reverse connection by means of a series diode, therefore incorrect
connection of the output wires will result in near zero current flow in the loop. Incorrect connection of
the sensor wires will result in the transmitter saturating at either its low or upper limits.
The diagram on the next page shows the method of connection to provide a (4 to 20) mA current loop
output. The Pt100 sensor shown would normally take the form of a probe assembly with a three wire
output. The output loop shows a 24 VDC power supply, used to provide loop excitation, the transmitter,
and a load all connected in series. The load symbol represents other equipment in the loop e.g. indicators,
controllers, loggers etc. Sometimes these instruments may come with the 24 V supply built in as standard,
this simplifies wiring and reduces cost.
Care must be taken when designing the (4 to 20) mA circuit to ensure that the total burden of the loop,
that is the total voltage requirements of all the equipment in the loop added together, does not exceed
the power supply voltage. If a number of transmitters are connected in the loop, ensure that only one
instrument is tied to ground. Grounding the loop at two points will result in shorting out part of the loop
and therefore any transmitters in that part of the loop will not operate.
Figure 3
Pt100
Zero Adjust
Span Adjust
RL
Load
+
V
-
Maximum load resistor, RL, is calculated as follows :
For 24 V supply :
RL = (V-10)/20 x 1000
RL = (24-10)/20 x 1000 = 700 Ω
3.3 EMC
This transmitter conforms with EC directive BS EN50081-1 and BS EN50082-1 when correctly installed in
a termination head providing at least IP20 protection and fitted with a sensor with less than 3 m of cable.
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