MR266 Automates Potentiometer-Based Controls

Micronor's MR266 remote-control rheostats and MR267 remote-control potentiometers are turn-key solutions for upgrading manual potentiometer-based process controls to automated PLC control. The products operate at 24V DC and offer a choice of 4-20mA or 0-10V input/output interface for compatibility with the broadest range of PLC, DCS, A/D, D/A and other control devices. Mounting options include front panel-mount (MR267 only) and DIN rail mount. The MR267 series replaces low power (less than 5W) potentiometers in the range of 100 to 100K Ohms.

The MR266 series replaces high-power rheostats in the range of 2.0 to 50K Ohms with four power options (20, 60, 170 and 300W). In addition to analogue input/output control, the MR266/MR267 series offer additional features. Three user-adjustable trimpots determine the min (4mA/0V input), max (20mA/10V input) and speed (10-120 seconds) set points. An override-mode option allows the system engineer to define how the unit shall respond when a user tries to manually override the unit via the front-panel knob.

Setting the override DIP switch to 'on' disables analogue input control until a reset is performed. The optional MR267A override pushbutton/LED indicator assembly is offered as a turn-key accessory for use with the override mode. Example application - a systems engineer wants to automate the speed control of a motor drive system that is manually controlled via a 2W potentiometer adjusted within the range of 10-85 Ohms. The engineer has a PLC interface available with 4-20mA programmable output. The user specifies an MR267 configuration with a non-isolated 4-20mA input and 100-Ohm potentiometer.

Upon receipt of the unit, he would then set min (4mA input) corresponding to 10-Ohm potentiometer setting and max (20mA input) corresponding to the 85-Ohm position. The factory default settings are: minimum 0 Ohms, maximum 100 Ohms and speed of 10s. The MR266 remote-control rheostat also offers a convenient way of relocating high power (hot) rheostats closer to the controlling equipment - for shorter electrical connections and better thermal control. Simply mount the MR266 unit in the environmentally conditioned instrument cabinet and then remotely control it from the operator's console via the optional HPFF front panel-mount control accessory.

The MR266/MR267 series remote-control rheostats/potentiometers operate from 24V DC with an operating temperature range of -15C to +65C and storage temperature range of -20C to +75C. High wattage rheostats may require temperature de-rating if operated near their power limits. In small quantities, a typical MR267 motorised potentiometer with non-isolated 4-20mA input costs USD995 (GBP684), with two- to three-week lead time. The typical MR266 series motorised rheostat configuration ranges are available from USD1,295 for 20W, USD1,495 for 60W, USD1,695 for 170W, and USD2,495 for 300W; four- to six-week lead time.

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