measurement & control 3

[jimmy55]

1) Is it possible to calibrate a dp transmitter in workshop below its minimum span limit. We purchased a transmitter range LRL = -10kpa and URL 10 kpa. Minimum span limit given on Tr was 5 kpa. We adjusted it to 2.5 kpa ( forgotten span limit) by applying pressure on + leg and leaving -leg in area. But when installed in field it started giving random values. Why ?



2) How I can calculate minimum plate thickness for flow element ?

3) Is someone help me to calculate dp for elbow type flow measurement?

 

[sgkb15]

I think you should refer the BS standard BS 1042 which gives the guidelines for sizing of orifice plates. However, I believe that the standard has since been superceded by a EN standard(European standard).<br>
<br>
As for calibrating a transmitter below its minimum span limit I will check and let you know if I can find or come across the answer. <p>Sandeep G Kusurkar<br><a href=mailto:kusurkar@vsnl.com>kusurkar@vsnl.com</a><br><a href=

http://education.vsnl.com/sandeepkusurkar/>Personal

& Educational Page of Sandeep G Kusurkar</a><br>

 

[merprorenegade]

Not sure about the recalibration of the pressure transmitter below the minimum span, but I would recommend you discuss with the manufacturer for best advise.

For the orifice plate thickness, forward your process data to an orifice plate manufacturer and they will advise the thickness of the plate. The thickness of the plate is generally dependant on the material of the plate, the maximum upstream pressure and the flow rate through it.

 

[juan8651]

In Foxboro web page you find a program to calculate y sizing
any flow element. Also in Fisher & Porter you can find all the neccesary literature for sizing this element.
I hope that this information to serve you.

 

[Premod]

Hi,
For orifice plate thickness i have a spreadsheet for reference which may be useful to you. I am not sure how you include an excel file in this post so if you let me know your mail address i could mail it to you.
The rangeability of transmitters is manufacturer specific but generally for the range of URL 10 kpa the rangeability would be around 10:1(with about 0.1% Calibrated span accuracy )that will help you set your DP as low as 1kpa for the accuracy of 0.1% of calibrated DP span. You could verify the exact rangeability with your supplier & also check the installation properly. Sometimes the problem is just due to a faulty installation.
No idea on elbow taps.
I hope this information helps.