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Join Date: May 2011
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Siemens Transmitter Absolute Pressure

04/30/2013 1:16 AM

hello ,

after I install the absolute pressure transmitter (Siemens 7mf4233-1DA60-1AB7-Z) I chose mode 7 and make the zero adjust!! My manager sure from I am doing wrong in doing that is he right or wrong ,and how to adjust the absolute PT

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#1

Re: Siemens transmitter absolute pressuer

04/30/2013 3:01 AM

It's all in the manual that came with it!

RTFM!

Unbelievable.

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Guru

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#2

Re: Siemens Transmitter Absolute Pressure

04/30/2013 8:17 AM

Mucking about with zero on an absolute pressure transmitter really does warrant reading the manual.

The mode 7 zero adjustment is intended for very slight zero offsets due to mounting orientation where the transmitter can be slightly off-vertical plumb. Implementing it takes pushing 2 buttons simultaneously, so one can't accidently initiate a mode 7 adjustment, because when you do, you've done it.

You really need to read the section 6.2.5 on zero adjustment in the manual.

It warns:

Then it gives several options for attempting to recover zero.

Modes 5 and 6 are normally used for defining the 4-20mA range.

Good Luck.

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#3

Re: Siemens Transmitter Absolute Pressure

04/30/2013 8:24 AM

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

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#4

Re: Siemens Transmitter Absolute Pressure

05/01/2013 9:23 AM

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.

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