Sunday, November 29, 2009

Signal Isolator Serves as Subtractor

Measurement and control applications sometimes need a difference (A - B) calculation. Examples include:
  • Liquid level measurement in a closed vessel. Level is proportional to the bottom liquid pressure minus the top ambient (gas or air) pressure.
  • Liquid blending control. Must maintain a zero difference between two measured flow rates.
  • Relative speed control. Control for zero difference between two speed measurements.
JH Technology offers a complete range of multiple input add/subtract instruments, but when the inputs are voltages a lower-cost isolator may do the job.
The figure shows two voltages, both grounded. The signals may come from two pressure or flow transmitters, tachometers or other sources. The isolator's input is connected between the two positive voltages; thus, the input is (V1 - V2). Its output may be set to equal the differential input or it may be scaled up or down, offset or converted to a current signal such as 4-20mA.
We offer plug-in, DIN rail and field mount style isolators and transmitters.

Links: Add/Subtract Transmitter Modules
DIN-Rail style add/subtract transmitters
All Process Transmitters and Alarms

No comments:

Post a Comment