Control.com - Nerds in Control

I have a composite DC drive that uses two motor controllers, one
for the armature and one for field. The original input devise for the speed control was a tandem pot that is no longer available. This was unique in how it was configured. The assembly rotated 320 degrees and the first half of rotation one pot changed value linearly and then remained at the high value through the rest of the sweep. The other pot has an inverse function where the start value is high and remains high for the first half of rotation and then drops in linear fashion to full travel.

I would like to use something to recreate this relationship of value with something that can produce a 0-10 VDC signal output. Driven by a single pot variable DC 0-10 volt input. The current requirement is signal power in the low mil amp range.

Sounds easy enough? Where do I start?

Feel free to contact me at stevenlemberg<at>sbcglobal<dot>net

Thanks,
Steve

Hello Steven,

Acromag offers two standalone signal conditioner options that might be
very interesting for you. Both can handle voltage input(s)/output and
offer custom functions to drive the output.

Model 892M-0500, IntelliPack Dual V/I Input Math Module. Programs like an "Excel spreadsheet" and includes conditional logic functions. Here is the link:
http://www.acromag.com/parts.cfm?Model_ID=73&Product_Func tion_ID=24&Category_ID=10&Group_ID=2

Model 811T-0500, IntelliPack Universal V/I Transmitter. Includes a 25
break-point custom linearizer function. Here is the link:
http://www.acromag.com/parts.cfm?Model_ID=67&Product_Func tion_ID=12&Category_ID=8&Group_ID=2

Other solutions would likely include using a PLC, DCS, or available
controller to get you the functionality you need I believe.

Kind Regards,

Donald Lupo
dlupo@acromag.com

Simple enough, use an A/D and use the value as an index to two look up tables and use their values to drive two D/A. You can program almost any function this way.

Regards

cww

Thank you gents,

Could you show me an example of an A/D device that could do this?

Thanks,
Steve

Any PLC with an analog input and two analog outputs could be programmed to do this. You would probably want to mask off some of the lower bits on the input to keep the number of steps reasonable. Just how to do it would depend a little on the individual PLC as arrays and other ways of construction a lookup table vary a bit, but pseudocode might be:
create two arrays of 1024 elements.
reduce 0-10v analog in reading to 0-1023.
read input
look up result 1 move result1 to output 1, something like
output1(array1(input))
same for output 2.

The loading of the arrays will vary also.

Regards

cww