6
Working stroke
The ranges of working stroke are given in Table No. 1.
Manual control
Manual control is performed by a hand wheel directly
(without a clutch)
and it is also possible when the electric motor
is running. By rotating the hand wheel in the clock-wise direction the actuator output pull rod is thrown out
(closes).
Torque-limit switches in the actuator are set and work when the actuator is under voltage.
When using the manual control, ie. actuator is controlled mechanically, the torque-limit switches doesn´t
work and the valve can be damaged.
5. ACTUATOR OUTFIT
Torque-limit switches
The actuator is fitted with two torque-limit switches
(MO – OPEN, MZ – CLOSE)
each of which acts only
in one direction of motion of the actuator output shaft. The torque-limit switches can be set to operate at any
point of the working stroke except the region in which they are locked
(see Starting thrust).
The tripping torque can be adjusted within the range shown in Table No. 1. The torque-limit switches are locked
if the load torque is lost after they have been brought into the OFF-position. This feature secures the actuator against
the so-called “pumping”.
Position-limit switches
The PO – OPEN and PZ – CLOSE position-limit switches limit the actuator working stroke, each being adjusted
to operate in either end position.
Position signalling
For signalling position of the actuator output shaft, two signalling switches, i.e. the SO – OPEN signalling switch and
the SZ – CLOSE signalling switch, are used. Each of these switches acts only in one direction of output shaft rotation.
The operating point of the microswitches can be set within the whole working stroke range except the narrow band before
the operating point of the microswitch used to switch off the electric motor.
Position transmitters
The
MODACT MTN, MTP electric actuators can be supplied without position transmitter can be fitted with position transmitter:
a) Resistance transmitter 1 x 100
Ω
.
Technical parameters:
Position scanning
resistance
Turning angle
0° – 320°
Non-linearity
≤ 1 %
Transition resistance
max. 1.4
Ω
Permitted voltage
50 V DC
Maximum current
100 mA
b) Type CPT 1Az passive current transmitter. Power supply to the current loop is not a part of the actuator.
Recommended feeding voltage is 18 – 28 V DC, at maximum loading resistance of the loop 500
Ω
. The current loop
should be earthed in one point. Feeding voltage need not be stabilized; however, it must not exceed 30 V or else
the transmitter could be damaged.
Range of CPT 1Az is set by a potentiometer on the transmitter body and its starting value by corresponding partial
turning of the transmitter.
Technical parameters of CPT 1Az:
Scanning of position
capacity
Working stroke
adjustable 0° – 40° to 0° – 120°
Non-linearity
≤ 1 %
Non-linearity, including gears
≤ 2.5 %
(for a maximum stroke of 120°)
Hysteresis, including gears
≤ 5 %
(for a maximum stroke of 120°)
(
The non-linearity and hysteresis are related to a signal value of 20 mA
)
.
Loading resistance
0 – 500
Ω
Output signal
4 – 20 mA or 20 – 4 mA
Supply voltage
for R
load
= 0 – 100
Ω
10 to 20 V DC
for R
load
= 400 – 500
Ω
18 to 28 V DC
