Configurable Double Limit Switch

General Description

This module contains two comparators and one or two relays for the monitoring of analog signals from 0-400 mV, 0-10 V or 0-20 mA. The input range, the operating mode, and the setting of the contacts can be programmed via DIL-switches on the rear of the unit.

  • Two switching thresholds with status LEDs, adjustment via a 12-turn potentiometer
  • Choice of one or two relays with double-throw contacts
  • Selectable operating modes: limit switch, window comparator, two-position controller
  • Programmable hysteresis (standard) and time delay (optional)



Modules for DIN-Rails

Type Input Relays Power Supply
COM 90-1 programmable 1 20-30V
COM 90-2 programmable 1+2 20-30V


  • Programmable via DIL-switches: 0-20 mA/100 Ohm input impedance, 0-400 mV/100 MOhm input impedance 0-10 V/250 kOhm input impedance.


  • 250 VAC/2 A max. switching voltage/switching current, max. 24 W/60 VA switching capacity, test voltage 1000 VAC. Gold-plated relay contacts also for µV/µA-signals.

Power Supply:

  • Max. current requirement with two relays is 80 mA.

Operating Mode:

  • The operating mode is selected via DIL-switches:
    1. One or two (relays 1 and 2) independent limiting values (thresholds).
    2. Window comparator (only relay 1).
    3. Two position controller (only relay 1).
  • Additional settings: relay inversion switching status, hysteresis (0.1-2% by trimming potentiometer).


  • Second relay (only for "high" limit)
  • Open input detection/current interruption (relay released)
  • Time delays (fixed or programmable)

When ordering, please specify:

  • COM 90-1 or -2 (with two relays)
  • DC-DC converter for the power supply
  • Basic version: COM 90-1 (with one relay), no DC-DC converter, no time delay

Operating Instructions

Setting of the Switching Limits, LED control light

The two switching limits, "high" and "low" are each set by a potentiometer (approx. 12 rotations) on the front plate. The three light diodes indicate whether the input signal lies below the "low" limiting value, between the two values (in the window between "low" and "high") or above the "high" limit value.

Setting the DIL switches

Input Switch Setting
0-400 mV 1 off 6 off
0-10 V 1 on 6 off
0-20 mA 1 off 6 on
Operating Mode Switch Setting
Simple limit value 2 off 3 off
Window comparator 2 on 3 off
Two position controller 2 off 3 on
Inversion relays 1 5 on  
Inversion relays 2 4 on  

Note: switches 2 and 3 must not simultaneously be "on".

Operating Modes

  1. Simple Limit Switch: the lower limiting value ("low") controls relay 1, the upper limiting value ("high") controls relay 2 (if present). The two limiting values (relays) are independent.
  2. Window Comparator
  3. Two Position Controller: The switching points (hysteresis) are set via the two limiting values "low" and "high". Applications include fullness controller ("low": on, "high": off).

Factory Settings

Hysteresis:ca. 0.5%
Operating Mode:Window comparator
Input:Voltage input 0-10 V

Note: when switching inductive loads (e.g., coils/transformers, motors) overvoltages occur which can lead to EMC problems and in some cases even to destruction of the relay contacts. These overvoltage spikes must be suppressed by suitable electronics at the load (e.g., RC-circuit or varistor).

Further Information