Theo V

Mismatch analogue transmitter to FX2N-4AD

5 posts in this topic

Hello all, I'm commissioning a project and connected a 2 wire pressure transmitter Danfoss MBS33 060G3039 to a FX2N-4AD module attached to a FX3U base.

When I connect a 4-20mA simulator it all works fine, my signal is correct 0-4000=4-20mA and my HMI shows a correct value however when i connect to the Danfoss transmitter a mismatch occurs. It starts with a 5,5mA signal at 0,0 BAR so my HMI shows already 1,0 BAR instead of 0,0. It seems, when I increase the pressure, that is is a linear up going signal. somehow I think it is a hardware connection because with the simulator at the input it works OK but I can not find an other way to connect than inthe manual. Is there an other way with resistors or something to allign the impedance to the PLC module?

Best regards,

Theo

E-diagram.jpg.jpg

PLC screenshot reading 4-20mA.jpg.jpg

PLC screenshot setting 4-20mA to all CH.jpg.jpg

Danfoss transmitter MBS33-060G3039.jpg

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The label suggests (Range of Pa) that it is an absolute pressure transmitter, not a gauge pressure transmitter.  So a 1.0 bar reading would be correct.

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OK, so I need to substract this enviromental pressure in the PLC program to have the proper readings.

I was worried about the mismatch that i would damage the PLC input but it seems normal. That gives me a good feeling that the installation will work fine for a long time.

Thank you for your quick reply pturmel.

Best regards,

Theo

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Well, it depends what you are measuring.  Ambient pressure changes with the weather, and that might be significant for your application.  If you expected a gauge pressure transmitter, you might need to change transmitters.

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Hi pturmel, Thanks for your suggestions about the ambient pressure. This Danfoss model is also used in the existing application so it won't be a problem to use it with the new controls. Today I've changed the program and made an offset [SUB...etc]  to have a more realistic value and it works fine so far. Thursday I will take the new installation live and keep the old controls as a back-up for a while so we have time to monitor and finetune during the day and switch back to the existing controls in the night or if it is not working well.

So far thanks for your input, I close the topic for now.

With best regards from Holland.

Theo V.

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