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ACTIONI/Q® Q438 DC Powered Potentiometer Input Signal Conditioner

Provides a DC Output in Proportion to a Potentiometer Input.

  • Accepts Potentiometers from 100 Ohms to 100k Ohms
  • Wide Ranging Zero and Span
  • ASIC Technology
  • High Density DIN Rail Mounting
  • Flexible DC Power Supply 9 to 30VDC
  • SnapLocTM Plug-in Terminals


The Q438 is a DIN rail mount, potentiometer input signal condi- tioner with 1800VDC isolation between DC power and the input/ output circuitry. The input provides a constant voltage and is designed to accept any three-wire potentiometer from 100 ohms to 100k ohms. The field configurable output is switch selectable providing a 0-5V, 0-10V, 0-1mA, 0-20mA or 4-20mA DC signal. Wide ranging, precision zero and span pots, used in conjunction with DIP switches, allow 80% adjustablity of offset and gain to transmit a full scale output from any 20% portion of the potentiometer input.

The Q438 is useful in transmitting process control setpoints to remote PID controllers or interfacing position or level sensors to data acquisition and control systems. The high density DIN rail mounting offers an extremely compact solution for saving valuable panel space.

In a valve positioning application a potentiometer is sometimes used as a feedback signal. Quite often a wide open valve is only a 25% turn of the feedback potentiometer. The Q438 can easily be adjusted with the zero and span to provide a fullscale output signal (e.g. 4-20mA) representing 0-25% or even 50-75% of the potentiometer input.

Unless otherwise specified, the factory presets the Model Q438 as follows:

Input Range:
0 to 100%
  4 to 20mA

For other output ranges, refer to Tables 1 and 2 to reconfigure switches SW1 and SW2 for the desired input and output ranges.

WARNING: Do not change switch settings with power applied. Severe damage will result!

Note: For best results, calibration should be performed with the intended output load, in the operating environment, mounted on a DIN rail, allowing at least one hour for thermal equilibrium of the system.

1. With power disconnected, set the output and input switch selectors (SW1 and SW2) to the desired ranges (see Tables 1 and 2).


2. Connect the input to a potentiometer. Connect the output to the actual device load (or a load approximately equivalent to the actual device load value) and apply power.

Note: To maximize thermal stability, final calibration should be performed in the operating installation, allowing approximately 1 to 2 hours for warm up and thermal equilibrium of the system.

3. Set the input to the desired minimum and adjust the zero potentiometer for the desired minimum output.

4. Set the input to the desired maximum and adjust the span potentiometer for the desired maximum output.

5. Repeat steps 3 and 4, if necessary.

Table 1: Input Range Settings

Table 2: Output Range Settings

Potentiometer Input:
End-to-end Resistance: 100 ohms up to 100k ohms
Input Impedance: >1M ohms
Input Excitation: 500mV, 5mA maximum drive.
Zero Turn-Up: 80% of full scale input
Span Turn-Down: 80% of full scale input
     Output: 0-5V, 0-10V
     Source Impedance: <10 ohms
     Drive: 10mA, max. (1k ohms min. @10V)
Current Output:
     Output: 0-1mA, 0-20mA, 4-20mA
     Source Impedance: >100k ohms
          0-1mA; 7.5V, max. (7.5k ohms, max.)
          0-20mA; 12V, max. (600 ohms, max.)
          4-20mA; 12V, max. (600 ohms, max.)
Accuracy (Including Linearity, Hysteresis):
0.1% maximum at 25 C
< 0.05%/ C maximum of full scale range
Response Time (10 to 90%):
<200mSec., typical
Common Mode Rejection:
120dB @ DC, >100dB @ 60Hz
1800VDC between line power and input, output
EMC Compliance (CE Mark):
Emissions: EN50081-1
Immunity: EN50082-2
Safety: EN50178
LED Indication (green):
Active DC power
Humidity (Non-Condensing):
Operating: 15 to 95% @ 45 C
Soak: 90% for 24 hours @ 65 C
Temperature Range:
Operating: 0 to 55 C (32 to 131 F)
Storage: -25 to 70 C (-13 to 158 F)
Consumption: 1.5W typical, 2.5W max
Range: 9 to 30VDC
0.48 lbs
Agency Approvals:
UL recognized per standard UL508 (File No. E99775)
CE Compliance per EMCdirective 89/3/36 EEC and Low Voltage 73/23/EEC






DC Output (+)


Not Used


DC Output (-)


Not Used


Not Used


Pot. Case Ground


Not Used


Pot. Input (fully CCW)


DC Power (+)


Pot. Input Wiper


DC Power (-)


Pot. Input (fully CW)

Ordering Information

Models & Accessories
  1. Model:   Q438-000
  1. Specify optional I/QRail, type and quantity
  2. Optional Custom Factory Calibration; specify C620 with desired input and output range.
  3. Accessories: (see Accessories)
ActionI/Q modules will mount on standard TS32 (model MD02) or TS35 (model MD03) DIN Rail. In addition, the following accessories are available:
MD02 TS32 DIN rail
MD03 TS35 x 7.5 DIN rail
IQRL-D002 2 Position I/QRail & DIN rail IQRL-D004 4 Position I/QRail & DIN rail IQRL-D004 4 Position I/QRail & DIN rail
8 Position I/QRail & DIN rail
WV905 24VDC Power Supply (0.5Amp)
24VDC Power Supply (1 Amp)
24VDC Power Supply (2.3 Amp)


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CTH Controls Inc.   CTH Controls Inc.
5100 South Service Road, Unit 2
Burlington, ON. L7L 6A5 Canada
Phone: 905-792-6829
Toll Free: 1-888-550-6829
Fax: 905-792-6902
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