Care must be taken when designing the 4-20mA 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 devices 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.
Maximum load resistor, RL, is calculated as follows :
RL = (v-8)/20 x 1000
For 24V supply :
RL = (24-8)/20 x 1000 = 800R
3.3 EMC
This transmitter conforms with EC directives BS EN 50081-1 and
BS EN 50082-2 when correctly installed in a termination head providing
at least IP20 protection and fitted with a sensor with less than 3 metres
of cable.
4.0 RANGES
This transmitter is normally supplied ranged 0 to 100ºC, unless a special
range has been requested at the time of order. With the aid of suitable
equipment, this transmitter can programmed to a different range by
following the simple procedure listed below.
4.1 Equipment
The following apparatus will be required in order to re-range the
transmitter:-
• Power supply voltage between 10-30 V DC, 30 mA min current
• RTD Calibrator or Precision resistance box (0 - 390R)
• Connecting cables
• 3 mm Diameter screw driver or similar device.
• Current meter 0 - 20mA to monitor loop current.
4.2 Method (See Figure 4)
1. Connect circuit as shown in Figure 4 and set the RTD calibrator for
temperature required at 4mA.
2. Press and hold the programming switch by inserting a 3mm diameter
screw driver blade through the programming hole, located in the top
face of the transmitter housing. Hold the switch for approximately 5
seconds, until the RED programming led flashes. Release the switch.
3. Set the RTD calibrator for the required temperature at 20mA. Allow
10 seconds settling time, then press and release the programming
switch. The programming LED will flash quickly for a few moments,
then go out. The transmitter is now ranged.
4. Check the transmitter output range is correct by setting the RTD
calibrator to the 4mA and then 20mA settings, checking the output
current reading on the meter.
4.3 Calibration Circuit
SEM523P
DIN RAIL MOUNTED
DUAL CHANNEL
TEMPERATURE
TRANSMITTER
Designed, manufactured and supported by
Green Lane Business Park
Green Lane, Tewkesbury
Glos. GL20 8DE. UK
Sales: +44 (0) 1684 296 818
Support: +44 (0) 1684 296 818
Fax: +44 (0) 1684 293 746
Email: [email protected]
Every effort has been taken to ensure the accuracy of this
specification, however we do not accept responsibility for
damage, injury, loss or expense resulting from errors and
omissions, and we reserve the right of amendment without
notice.
Stock code: 52-214-2320-01
Issue: A
R
B o x
1 0 -3 0 V D C
m A
0 V
C H 1
C H 2
9
10
11
12
8
7
1
2
6
3
4
5
SW IT CH
LED
Figure 3
Burnout
Due to the sensing method, certain combinations
of open circuit sensor wires may result in the
output current dropping for approximately 500mS,
before rising to upscale output.
