Daft question about pressure transmitter range
Daft question about pressure transmitter range
(OP)
Hi Gents,
I'm going to show my ignorance here, but hopefully you'll be gentle with me.
I believe that ideally a pressure gauge should be sized so that the needle is in the middle of the range when reading normally - i.e. if I have 5 barg pressure then a gauge of 0 ~ 10 barg range would be optimum, whereas say a 0 ~ 100 barg range would be inadvisable because of the inaccuracy of both the reading and the instrument itself at that low end of the scale.
So my question is, assuming the above to be correct, does the same apply with a Rosemount Pressure Transmitter? In the particular case in question, I have been supplied a 0 ~ 150 barg transmitter on a systekm with a maximum pressure of around 10 barg, and a working pressure of 2 ~ 4.5 psig.
My intention is to reject it, but I don't want to make a fool of myself (any more than I possibly am already in asking the question here!!!!!).
Any input much appreciated.
I'm going to show my ignorance here, but hopefully you'll be gentle with me.
I believe that ideally a pressure gauge should be sized so that the needle is in the middle of the range when reading normally - i.e. if I have 5 barg pressure then a gauge of 0 ~ 10 barg range would be optimum, whereas say a 0 ~ 100 barg range would be inadvisable because of the inaccuracy of both the reading and the instrument itself at that low end of the scale.
So my question is, assuming the above to be correct, does the same apply with a Rosemount Pressure Transmitter? In the particular case in question, I have been supplied a 0 ~ 150 barg transmitter on a systekm with a maximum pressure of around 10 barg, and a working pressure of 2 ~ 4.5 psig.
My intention is to reject it, but I don't want to make a fool of myself (any more than I possibly am already in asking the question here!!!!!).
Any input much appreciated.





RE: Daft question about pressure transmitter range
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Daft question about pressure transmitter range
Kind of yes and no. You need to find out exactly which transmitter has been ordered and what it said on the data sheet. Rosemount supply their transmitters in a set of pressure ranges. Normally the specific range is then set on site to decrease the uncertainty, e.g. if you have their standard range 3 (0-55 bar) you would calibrate the maximum value to above wha your max value is supposed to be, just so that if it ever exceeeded the max value, your transmitter wouldn't just "max out", so probably 12 barg in your example. This reduces the uncertainty in that range 0-12 bar. However if tou have a transmitter with an inital much bigger range, then this may not apply. Find the exact model number with all its digits or serial number and then give rosemount technical salses a call and describe your issue and whether a different ranged transmitter would be better or not. What you're asking is a fair question, but the best answer will come from the vendor.
ALways make sure that the transmitter is an indicating transmitter - the additional cost over non indicating is marginal, but the benefit when you're walking around a plant trying to work out what's going on is enormous and helps reduce the number of guages which suffer from the problem you mention over range.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Daft question about pressure transmitter range
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Daft question about pressure transmitter range
RE: Daft question about pressure transmitter range
If you can recalibrate it to 0-100 psig then your uncertainty will be +/-0.5 psig which might be OK. Calibrating it for 0-25 psig would give you +/- 1/8 psig which would be better.
It has been a few years since I actually did this, and the technique could easily have changed, but back in 2000 you would put a 25 psig physical pressure into the device and crank the current to 20 mA. Then verify that 12.5 psig was 12 mA, etc. It really was that easy back then. I do not know if manufacturers have backed off that and put a switch within the device to select specific ranges (which feels like a major step backwards to me).
David Simpson, PE
MuleShoe Engineering
"Belief" is the acceptance of an hypotheses in the absence of data.
"Prejudice" is having an opinion not supported by the preponderance of the data.
"Knowledge" is only found through the accumulation and analysis of data.
The plural of anecdote is not "data"
RE: Daft question about pressure transmitter range
You can either ask the designer / vendor / supplier to provide you with details of the accuracy of the transmitter at your working range or do a bit more homework with Rosemount before you go back to them saying - I've checked with rosemount and they tell me I need a XXX-YYY model - Please supply the right part. If you have the rosemount transmitter model no then you can do a lot yourself or just ring them up, describe your process cnditions and ask them what is the right one.
My motto: Learn something new every day
Also: There's usually a good reason why everyone does it that way
RE: Daft question about pressure transmitter range
RE: Daft question about pressure transmitter range
I've hovered around the forum for a while now and even try to help out occasionally where Meccy seals are concerned, but instrumentation has always been a bit of a black art to me!!
Thanks again.
Paul.