Micronor: Motorized ‘pots’ with 4-20 mA input control

By Control Engineering Staff December 21, 2005
Micronor’s MR267 CLC option operates from commonly available 24 V dc and has an operating temperature range of -10 to 65 °C.

New MR267 Current Loop Controller (CLC) option from Micronor remotely controls a motorized potentiometer and/or rotary cam switch via 4-20 mA current loop, 0-2.5 V input, or external potentiometer. MR267 reportedly offers a simple, inexpensive way to automate existing systems controlled by manually operated potentiometers, rheostats, or rotary cam switches.
Motorized potentiometers (and rotary cam switches) are simple to set up, use, and maintain, and they work without the need for computers or software, says the company. User-specified potentiometers provide absolute position feedback or serve as a variable resistor in an analog control or bridge circuit. Motorized “pots” add a smooth uniform ramp throughout the timing cycle. Typical applications include dc motor field current ramping and start-up control of a generator.
These products are available in a wide variety of configurations. When the CLC option is specified, the MR267 control board, a MR267-dedicated rotational feedback pot, and 12-V dc motor are added to the configuration.
Associated firmware incorporates three trimpots, used to alter the motor pot’s normal operating mode and scale. For applications where analog control circuits operate only within a narrower region of a pot’s full scale range, POS A and POS B trimpots are used to program positional offsets corresponding to the lowest (4 mA) and highest (20 mA) input values. A third trimpot, SPEED, allows fine adjustment of the timing cycle.
Pricing for typical MPP Series single-turn motor pot configuration with two cam switches and MR267 option is $612, each, in small quantities (available 2-3 weeks ARO).

Frank J. Bartos, executive editor, Contol Engineering