Pressure Trasnsmiter*

[garciaf]

Here is my issued
I have a pressure transmitter ST700, Honeywell, the range of the instrument goes from 0 to 500 PSIA {SEE IMAGE ATTACHED}, the pump associated to the pressure trasnmitter is located in the suction line of this pump, Q iqual to 170 m3/h, H iqual to 56.3 m. in the suction line there is also a local manometer that shows 2inHg [Vaccum], 0-30 psig [pressure].
what I want to konow is the following
This pressure transmitter range is correct for my aplication, I think is ok, because the range instrumente covers 0 PSIA THAT IS -14.7 psig to 500 PSIA [485.3 psig], with my HART I CAN CONFIGURE THE INSTRUMENT IN A RANGE THAT I CAN SET IN THE RANGE FOR EXAMPLE OF 0 PSIA TO 50 PSIA THAT INSIDE THIS RANGE THE INSTRUMENT IS GOING TO WORK, SENDING THE ANALOGIC SIGNAL [4-20mA].

THE TECHNICHIAN SAID THAT THE PUMP CREATES TOO MUCH VACUUM AND DAMAGE THE DIAPHRAM OF THE PRESSURE TRANSMITTER, I DONT THINK SO.
I AM NOT A INSTRUMENT ENGINEER, BUT RIGTH NOW IS MY JOB.
PLEASE HELP ME.
IF I SAID SOMETHING WRONG PLEASE CORRECT.
THANK YOU SO MUCH FOR YOUR TIME

 

[Compositepro]

Full vacuum will not damage the instrument but its accuracy will be greatly diminished compared to an instrument with a 50 psia range. Would you use a 12" ruler to measure something that is 0.1" long to a 0.001" accuracy?

 

[garciaf]

Thanks for your answer.
In other words is that the range of the instrumt is too much high, due to the application of it.
Would be the best an instrument that measure from 0 PSIA to 40 PSIA, and the accuracy would be the best, because the instrument I have will tend to get more error, and the measure is not going to be precise.

 

[Compositepro]

That is correct. But you must also consider what the maximum possible pressure is in the pipe so the instrument is not damaged by peak pressures.

 

[roydm]

You need to post a simple Process and Instrument Diagram showing where the transmitter is located and what it is doing.

From your description it's in the pump suction, it's hard to imagine why you would need a 500 psi transmitter there.

If the transmitter is connected to pump discharge will be about 80 psi if it's water you are pumping.

It's not usual to use an absolute pressure transmitter unless the process is one effected by atmospheric pressure like a condenser for example.

 

[georgeverghese]

Try to get as close a fit of the operating pressure range to the calibrated range of the PT to give you good accuracy. For operating pressures that may be just below or just above atmosperic pressure, then the elevation of the PT diaphragm wrt to the process line should also be taken into account in the bias.

 

[danw2]

That STA74L is the correct model transmitter for your 0-50 PSIA application.

It's a smart transmitter, fully capable of meeting its accuracy spec for a 10:1 turndown (500 URV : 50 URV). The model with the next lowest range is 0-15 PSIA range model, too low a range for your application.

It is an absolute pressure transmitter specifically designed to handle vacuum pressure on the diaphragm. The technician is misinformed about how this transmitter can be applied.

Your statement,
"with my HART I CAN CONFIGURE THE INSTRUMENT IN A RANGE THAT I CAN SET IN THE RANGE FOR EXAMPLE OF 0 PSIA TO 50 PSIA THAT INSIDE THIS RANGE THE INSTRUMENT IS GOING TO WORK, SENDING THE ANALOGIC SIGNAL [4-20mA]."
is correct.

 

[garciaf]

THANKS FOR ALL YOUR ANSWERS.
THE INSTRUMENT ENGINEER WHEN THE PROJECT WAS IN COURSE THE SUPERVISION WAS SO BAD THAT THEY DID NOT NOTICE THIS.
IT WAS AN ERROR, UNFORTUNATELY.
I WILL TELL THE TECHNICIAN ABOUT THIS, HE IS WRONG ALSO.

 

[silverlily]

good post to share , and learn a lot from above answers.i am always learning a lot on pressure transmitters.

Silver automation Instruments

http://www.silverinstruments.com