SEM104TC Datasheet, PDF (7/8 Pages) List of Unclassifed Manufacturers – SEM104 SERIES

3.2 ELECTRICAL
Connections to the transmitter are made to the screw terminals provided on the top face. No special wires
are required for the output connections, but screened twisted pair cables are recommended for long runs.
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 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, depending on the
setting of the burnout links.
The diagram shows the method of connection to provide a (4 to 20) mA current loop output. The TC sensor
shown would normally take the form of a probe assembly with a two 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, normally indicators, controllers, loggers etc.
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 instruments 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 the instruments in that part of the loop will not operate.
NOTE: The thermocouple used with this transmitter MUST be isolated from ground. If a grounded
thermocouple is used, measurement errors will occur.
Figure 3
THERMOCOUPLE
UNGROUNDED
JUNCTION
COLD JUNCTION
ZERO ADJUST
V
SPAN ADJUST
RL
LOAD
Page 11
4.0 RANGES
This transmitter is normally supplied as one of the standard ranges,refer to data sheet. Other ranges can
be supplied at time of order but with the aid of suitable equipment, the user can re-range the transmitter.
On board links allow the transmitter to be re-ranged to operate over most common industrial and commercial
ranges.
WARNING!
Re-ranging requires the soldering of small links located on a pcb, housed inside the
transmitter. The operator must be experienced in soldering and un-soldering
techniques on small PCB, or damage may occur to both PCB and enclosure. If in
doubt please state the required range at the time of order, to allow the factory to
calibrate for you. It is the users responsibility to ensure that no damage occurs due
to lack of care during this re-ranging procedure.
PROCEDURE
Before you start you will need the following equipment :
TC calibrator with internal cold junction compensation
DC milliamp meter (digital); accuracy 0.05 % on (0 to 20) mA range
Power Supply; 24 VDC 30 mA minimum
T/C Compensating wire, wire for (4 to 20) mA loop, plus trim tool
Soldering iron with fine tip, solder. De-soldering tool.
STEP 1
Decide on the range you require and ensure the transmitter is capable of this range. If a range
has not been specified at time of order, the transmitter will leave the factory set as type K,
(0 to 1000) ºC. Obtain access to the internal PCB by flipping out the base cover, using a small
screw driver. Remove any pre-solder links from positions A, B, C, D, X, Y, Z, and J.
STEP 2 Let
TL = offset
Locate offset TL on Table 1 and solder blob indicated links.
STEP 3 If TC type is “J” then solder blob link “J”
STEP 4 Let
Tl = Required Temperature @ 4 mA
Let
Th = Required Temperature @ 20 mA
Calculate Transmitter Span Ts = Th - Tl
Locate span Ts on Table 2 and solder blob links indicated.
STEP 5 If down scale burn out is required, un-solder link “U” and solder link “D”. (If up/down scale
burnout is not important then remove both links U + D)
STEP 6
Connect T/C calibrator to +/- input terminals. Ensure wires are the correct type and polarity.
Connect + signal terminal to + power supply terminal. Connect mA meter in series with the
return wire from the - signal terminal to - terminal on power supply. Turn on. Allow a few
minutes before calibration to allow the cold junction to stabilise, after the effects of handling
the transmitter. Avoid touching the input terminals and wires during calibration as this will cause
errors in the cold junction tracking.
STEP 7 Set calibrator to temperature Tl and adjust “Z” potentiometer for 4.00 mA output ± 0.01 mA.
Page 12