Looking for a 4 or 8-channel converter for 4-20mA inputs and 0-135Ohm outputs

[AdaptnOvercome]

Problem:

Our PLC can only output 4-20mA, but the actuators it needs to control, modulate based on a 0-135Ohm signal. Buying 4 or 8 individual converters like DRN's is a solution, but we are looking for a more compact (and hopefully less expensive) solution. Replacing all of the actuators with ones that have a different control signal is not an option we have.


I've looked high and low and can't find anything but single channel signal conditioners for converting 4-20mA to 135Ohms. I did find an 8-channel device with 4-20mA inputs and -10V - 10V outputs, but I'm not sure how to get a 0-135Ohm output from a 0-10V output. Any help would be appreciated.

 

[robertmee]

0 to 135 is common in Boiler and HVAC, and are usually single controllers, so finding a multi channel solution will likely prove fruitless. Most are single converters designed to fit inside the manuf particular valve. The DRN series by ACI is probably the most abundant.

 

[busarider29]

ARM | Automation Components, Inc.

All I could find, but you likely found this already.

 

[ojz0r]

You can DIY with leds and LDRs (light dependant resistors) in shrink tube, but its a dirty solution and will be effected by surrounding temperature and wire resistance.

 

[Puddle]

Motorised potentiometer? Unlikely to find a unit on the shelf now so would have to build one, but these are basically a tiny motor attached to a rotary potentiometer with relay control to turn each way to adjust the reading.

 

[TWS]

Watch this: HVAC Tech School: The Easy Way to Convert 0 -135 ohms to 4 - 20ma.

 

[FilthyTech]

Check out PCB Piezotronics. They may have something that fits what you are looking for.

 

[AdaptnOvercome]

Thank you all for your responses. I did find the ARM and ACI products but they were all single-channel.

From my experience, the most popular actuator that uses a proportional 135ohm modulating signal is the honeywell modrutrol motor. They are heavily used in heavy commercial/industrial heating applications including burner firing rate, draft dampers, air louvers, feedwater valves etc.

https://www.supplyhouse.com/Honeywell-M9174C1025-120V-Non-Spring-Return-Foot-Mounted-Actuator-w-2-internal-aux-switches-75-lb-in?utm_source=google_ad&utm_medium=shopping_neutral&utm_campaign=Shopping_Neutral_Returning_users&gad_source=1&gclid=CjwKCAiAi6uvBhADEiwAWiyRduZPTV8kMqoU5BVca6MvIuxs5lfXdFEnu-5u814IFBW1cEt41E4GfRoCnZUQAvD_BwE

Here is the solution we ultimately found in case anyone was curious.