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I have a pressure sensor giving an output of 1-5 Volts. My PLCs analog module takes an input of 0-10V. It's an 8 bit Module (0-255). The pressure sensor has a measurement range of -760mmHg - +760mmHg. The normal operation of my process is from 0 mmHg to -110 mmHg. In this case, which is better....to change the sensor or to use a high resolution analog module?

If -760mmHg to +760mmHg corresponds to +1 to +5 volts, then your working range of 0 to -110 mmHg will produce a span of 0.289 volts. Reading that through an 8-bit A/D converter that is expecting 0 to +10v will transform that 0.289 volt span into a span of only 7 counts. I don't know what resolution you need in your application, but I'll bet it is more than 7 discrete levels.

As for your two solutions, either one will work. But getting a different sensor has the advantage that electrical noise will be easier to manage. You may end up needing to do both - get a different sensor and get a higher-resolution A/D.

Robert Scott
Real-Time Specialties
Embedded Systems Consulting

The conventional answer is to a signal conditioner to change the 1-5 volts to 0-10V. If you are really only using part of the range, you could even expand the signal more so that 0 - 110 mmHG (or whatever is suitable) is 0-10V. You just need to use a signal conditioner that has that much adjustment range. This much adjustment though would require a signal conditioner that has multiple range jumper settings plus potentiometer adjustment for fine tuning.

Thank You Friends for your valuable suggestions.