1800IF - PAGE 16 OF 19
Valvcon Corporation
http://www.valvcon.com
phone: 603-249-9020 fax: 603-249-9140
Fail Last Position
Normally, if the positioner senses a complete loss of control signal, it will cause the actuator to go to the fully
closed position. However, the positioner can be calibrated to provide "Fail Last Position". If this feature is used,
the actuator will simply stay in its present position when there is a complete loss of control signal.
The procedure to calibrate the positioner for "Fail Last Position" is as follows:
1. Determine the minimum level of control input signal that will define loss of signal. (For example, in a 4 to 20 mA
system, a control signal of 3.5 mA or below is considered to represent loss of signal.)
2. Apply this minimum level of control signal to the positioner. The actuator will move clockwise stopping at the
fully-closed position with the RUN and CW LED's illuminated.
3. Adjust the LIM potentiometer until the CW LED turns off, and the RUN LED remains illuminated.
NOTE: For voltage or resistance input signals, the "Fail Last Position" feature can still be used. First, the minimum
signal to be used in normal operations (which is usually zero volts or ohms) must be increased above zero. This
means that the normal range of control signals will be about 1 to 10 volts or 30 to 1000 ohms. Then apply less
than 1 volt or 20 ohm signal to the positioner, and adjust the LIM potentiometer as described in step 3 above.
Once this has been completed, if the positioner senses an input signal below 2 volts or 20 ohms, the actuator will
simply stay in its current position.
If the "Fail Last Position" option is not to be used, the LIM potentiometer should be kept in it’s fully CCW position.
Split Range Operation
Split range operation, where a single controller controls two positioned actuators to achieve a full range of control,
can be accommodated by the standard capabilities of the Valvcon Electronic Positioner. The regular ZERO and
SPAN adjustments in one positioner, is set to operate at, for example, 4 to 12 mA. The regular ZERO and SPAN
adjustments in the second positioner, is set to operate at 12 to 20 mA. The results achieved are shown below:
Input Signal: 4 mA 8 mA 12 mA 16 mA 20 mA
Actuator #1 Closed 1/2 Open Full-Open Full-Open Full-Open
Actuator #2 Closed Closed Closed 1/2 Open Full-Open
Supervisory Circuits
Supervisory circuits can be used to cause the positioner to ignore commands from the controller. This is achieved
by wiring a set of normally open contacts (switch or relay) to terminals T-16 and T-17 . This wiring should be
shielded with the shielding connected to the actuator housing. The wire should not exceed 5 feet in length.
Closure of the contacts will disable the positioner outputs and cause it to ignore commands from the controller.
With the supervisory circuit enabled, you can energize terminals 3 and 4 to actuate counterclockwise and
clockwise, respectively.
Reverse Acting
The positioner may be set up to operate in a reverse acting mode (to open on a decreasing control signal and
close on an increasing control signal).
The procedure to achieve this mode of operation is as follows:
1. Unplug the feedback potentiometer plug from the positioner board. Reverse the position of the red and green
wires. (This requires using a small screwdriver to depress the small tabs that lock the wires into the plug.)
Reconnect the plug to the positioner board.
2. Unplug the motor wiring plug from motherboard socket S-3. Reverse the position of the red and white wires,
using the same technique as described above. Reconnect the plug to the motherboard.
3. Reverse S1 and S2 on the motherboard.
4. Calibrate the positioner using the ZERO adjustment to set the fully open position (4 mA), and the SPAN
adjustment to set the fully closed position (20 mA). Always adjust the ZERO adjustment first.
Trouble Shooting
If the actuator fails to operate:
1. Check the control signals and connections at terminals T-18 and T-19. If the control signals and continuity are
correct, check the AC power at terminals T-1 and T-2.
2. If the control signals and AC power are correct, vary the control signal and observe the RUN, CW, and CCW
LED's. If they light as they should (see LED Indicators Defined), check motor and limit switch connections.
3. If the actuator still fails to operate, remove the positioner board, and check operation in both directions with
temporary connections between T-1 and T-3, then T-1 and T-4.
