Siemens Transmitter Absolute Pressure

I went through the same predicament when I first tried calibrating an absolute pressure transmitter. The manuals that came with them didn't mention what I'm going to telling you now.

First, let's assume you're at sea level. An absolute pressure transmitter has -1 barg as its zero or lower range limit and 0 barg as its span or upper range limit.

If you go and press "zero" (or whatever procedure it takes to zero the unit) without applying -1 barg to the transmitter's ports, you will be telling the transmitter that it is sensing -1 barg while it is actually sensing 0 barg. Your transmitter will then have an offset of 1 bar. You will end up with a transmitter that is reading 0 bara when the actual pressure is 1 bara.

I'm not sure if that makes sense to you. I had a hard time understanding my own writing. (",)

The biggest problem here is that there is no vacuum pump capable of creating a 1 bar vacuum. The best I ever got is 0.13 bara. The Foxboro service rep suggested that I calibrate the absolute pressure transmitter from 0 to 1 barg (gauge pressure) and then rerange the unit so that it reads correctly.

regards,

Vulcan

When you are working with specialty instruments or applications you need to have available two things:

1.- The latests and correct documentation, manuals, IOM, etc.

2.- You need a good calibration tools, certified so that you can verify what you are doing.

In this case you may need a good quality barometer to verify the zero setting, even before you do anything. It maybe correct, remember barometric changes will affect an absolute pressure transmitter.