16
Current position transmitter CPT 1Az – setting
Before starting setting the current transmitter it is necessary to set the end-limit positions
(torque or position
switches)
of the actuator and connect them into the tripping circuit of the electric motor. In case of an external source
of feeding voltage, verification must be carried out that it does not exceed the maximum value 30 V DC
(limit value
when CPT 1Az is still not damaged).
Recommended value is 18 – 28 V DC.
Positive pole of the source is connected to the positive pole of the transmitter CPT 1Az; a milli-ammeter of precision
at least 0.5 % connected into the circuit. The current loop must be earthed in one point. The figure does not show the
earthing that can be made at any point of the circuit.
1. Shift the output shaft into the position Closed. During closing, the current signal value should decrease. If it increases
release the transmitter body and, by turning of about 180°, shift to the descending part of the outputcharacteristics.
Set 4 mA by fine turning. Tighten the shim plates to secure the transmitter against spontaneousturning.
2. Shift the output shaft to the position Open and set 20 mA using a potentiometer on the transmitter body.
The potentiometer has a range of 12 revolutions and it has no stops so that it cannot be damaged by furtherturning.
3. Once again verify the current value in the position Closed. If it has changed too much repeat the points 1.
and 2. If the required corrections are large this procedure should be repeated several times. After
the setting, securethe transmitter against turning and drip the screws with varnish.
4. Use a voltmeter to check the voltage on the CPT 1Az terminals. In order to keep linearity of the output
signal the voltage must not drop below 9 V, not even with off-take 20 mA. If this condition is not met it is
necessary to increase the feeding voltage
(within the range of recommend values)
or to decrease total
resistance of the current loop R.
Caution!
The transmitter CPT 1Az must not be connected without checking the supply voltage. The transmitter outlet
conductors must neither be connected to the electric actuator frame nor to the earth, not even accidentally.
Before the supply voltage is checked, it is first necessary to disconnect the transmitter from the supply
mains. Measure the voltage on terminals of the electric actuator to which the transmitter is connected – this
can best be done using a digital voltmeter of input resistance at least 1 M
Ω
. This voltage should fall within
the range of 18 – 25 V DC; in no case may it exceed 30 V
(otherwise the transmitter can be damaged).
Then,
connect the transmitter so that the positive pole of the power source is connected to the positive pole of
the transmitter, i.e. to the pin with red insulator
(r)
+
(nearer to the transmitter centre).
The terminal with
white coating
(wired to the terminal 52)
is connected to the negative pole of the transmitter
(white insulator).
In the latest design variants the red conductor is plus and the black one is minus.
A milli-ammeter, preferentially a digital one with accuracy at least 0.5 %, is temporarily connected in series
with the transmitter. The output shaft is moved to the position CLOSE. The signal value should decrease. If this
is not the case, the output shaft should be rotated in the CLOSE direction until the signal starts decreasing and
the output shaft reaches the CLOSE position.
Then, loosen the screws of the transmitter shim plates so that the whole transmitter can be turned to set the current
to 4 mA, and retighten the screws of the shim plates. Thereafter, move the output shaft of the electric actuator to
the position OPEN. Using the resistance trimmer on the transmitter face
(nearer to the edge)
set the current to 20 mA.
The trimmer has 12 turn and no stops. Hence, it cannot be damaged.
CPT 1Az
U
U
R
mA
V
R
red
51
51
52
52
red
white
white
CPT 1Az
