Let me start off with that I am starting out on Instrumentation concerns so this may be a easy fix for those that are veteran Instrument Tech's.
I am attempting to adjust the readings on a 3051 Emerson-Rosemount differential Pressure level transmitter that has a 12ft lead running off of the Low pressure side of the base.
I have run tubing to a mounting area at the top of the tank and tied the lead to this point. The High side is directly bolted to the bottom flange on the tank. This a new sensor and I believe factory calibrated. When the sensor is running in the process it does not read as per the redundant ultrasonic sensor on the tank. It is reading considerably lower and is indicating a negative level at the lower range. How do I adjust this reading using a HART comm. ??
Is the medium in the tank water? What is the medium in the tank? Its specific gravity is?
Which head pressure units are you using? inches water column?
Are you reading level at some receiver device, like an indicator/controller/DCS/PLC?
If so, which level units are you using?
What is the transmitter's current LRV and URV?
> Is the medium in the tank water? What is the medium in the tank? Its specific gravity is?
> Which head pressure units are you using? inches water column?
Yes Inched H20
> Are you reading level at some receiver device, like an indicator/controller/DCS/PLC?
at the 3051 rosemount and the DCS.
> If so, which level units are you using?
The DCS is seeing it as a % and the indicator is in Inches H20
> What is the transmitter's current LRV and URV?
-250& 250Inches of H20
Negative values are common when capillary remote seals are used. You have not mentioned capillary remote seals.
Does this particular transmitter have one or two capillary remote seals?
- the elevation of the transmitter with respect to the lower seal position
- the elevation of the upper seal
- specific gravity of fill fluid
is needed to calculate LRV,URV
If there are no capillary remote seals, then your LRV should be zero.
Your URV should be = maximum physical level elevation (inches) * 1.51
example: 100 physical inches level will produce a head pressure measurement of 151" because of the density-specific gravity of the liquid.
100 (physical) inches * 1.51 = 151" measured inches w.c.
The DCS can interpret the 4-20mA as zero to the max physical level, zero to whatever, or 0-100%.
There is one capillary seal on the low side.
The lead is 12 ft long, so the transmitter is 12ft below and is flanged on the tank for the high side. The fluid in the tank is Sodium Hydroxide with a SpGr of 1.51. The fluid in the capillary I am not sure of and will check out the Instrument data when I get back in to the plant.
I also have a data sheet at my shop, of the standard elevation of ground and can figure that when in.
Thanks for all this help, I generally do Electrical and am attempting the Instrumentation to grow in the work force.
Thanks for you info Dave.
I have one capillary, Low side and will have to look into the medium for it. It was already installed when it became my problem. So I will have to do some "Research" on the Spec's for it.
The LRV and URV have to be calculated.
- the remote seal flange with capillary is mounted at the bottom (or close to the bottom) of the tank (true?)
- a 12ft capillary connects to the high side of the transmitter which is 12.00 ft in elevation below the flange? (this difference in elevation is critical, it needs to be measured)
- unfilled, empty tubing connects the low side of the transmitter to a point somewhere at the top of the tank? (True?)
> 12ft lead running off of the Low pressure side of the base. <
I'm not clear what that statement means. Can you clarify?
> I have run tubing to a mounting area at the top of the tank and tied the lead to this point. <
Is the tank pressurized? Does the tubing enter the tank so it can sense the pressure, or is it open to the atmosphere?
For the line/piping (empty tubing?) that connects from the low side of the pressure transmitter to the high side of the tank, is there a drop leg (with drain plug) installed near the transmitter so that condensation that will form in the tube will fall into the drop leg and not collect and apply pressure to the low side diaphragm sensor?
I have a 12ft Capillary off of the low side and it is connected to tubing a the top the tank that is pressurized via a nitrogen blanket, so the capillary does sense the tank pressure. The pressure from that blanket is 1.5Psi from the line.
I have a drain installed at both high and low sides.
So with respect to URV the I have calculated it to be 217.44inches, (12ft times the SpGr of 1.51, then converted to inches).
I am assuming the LRV would be the applied pressure from my nitrogen blanket, (1.5 psi which would be 41.56 or 1.5times 2.3089, which is the factor of 1 psi to feet of water column then converted to inches of H20.)
The nitrogen blanket pressure does not figure into the calculation, the DP transmitter sees that pressure on both high and low side ports and cancels it (high side minus low side).
As an example:
With the transmitter flange mounted at the bottom (transmitter high side port) and 12' low side port capillary filled with DC200 fill fluid (SG 0.94) mounted at 140" elevation above the bottom flange, the LRV and URV for a 130" physical level span (130" hydroxide (SG 1.51) level above the center point of the lower flange) would have an LRV of -131.6" and a URV of 64.7".
That's a span of 196.3"w.c. which = 130" (physical) * 1.51 (SG) with the applied static pressure of the capillary fill taken into account.
Mounting points (in elevation), fill fluid SG, and maximum fluid level do play a role in calculations.
Hey Newbie....here's a link to a manual that I think you will find useful..its the Rosemount 1191, pretty similar to what you have, and it will give you maybe's a clearer picture of how to go about setting these beasts up...their bark is worse than their bite, honest!
Read the book, crunch the numbers and bang them in with the HART...depending on the software version installed in your communicator, you might only be able to access some of the parameters. so best to start off with a model 375 communicator at the very least
Perhaps I am missing something but here goes. You appear to have a dp transmitter to measure simple pressure in a tank. I say DP because you mention a low side of the transmitter telling me there is also a high side. (As an instrument tech. knows, A simple pressure transmitter often used for tank height measurement has a single 1/4" npt female plumbing point. DP transmitters have 2 ports, a high and a low, often used in flow for an orifice plate or venturi tube where the incoming side of the venturi (where flow comes FROM) is connected to the high side and the outgoing portion of the venturi(on the system side(where the flow is going to) is connected to the low.
Now a DP or 2 port Can be used for simple height measurement. Forget whether you are feeding a dcs, plc, or other device. Focus on your transmitter output in mA or Volts.
Plumb your tubing from the BOTTOM of the tank (This gets into offsets depending on how close to exact bottom you get) Vent the transmitter Low side to atmosphere and if you have a calibrated transmitter to say 0 to 100' you will have 4 mA at a zero pressure and 20 mA at full 100' tank. I brushed past scaling, type of liquid, offset and other specifics here and decided to stay generalized and not go too deep.
> Vent the transmitter Low side to atmosphere
Well, this all went down 3.5 years ago, so it's now a moot point, but this application is not a 'vent-low-side-to-atmosphere application.
He was properly using a DP transmitter with the low side connected to the nitrogen atmosphere blanket so the nitrogen pressure could be subtracted from the high side pressure to produce a head pressure.
>> Capillary off of the low side and it is connected to tubing a the
>> top the tank that is pressurized via a nitrogen blanket, so the
>> capillary does sense the tank pressure. The pressure from that
>> blanket is 1.5Psi from the line.
"When the sensor is running in the process it does not read as per the redundant ultrasonic sensor on the tank. It is reading considerably lower and is indicating a negative level at the lower range"
Here's a slightly different way of calibrating it not that other methods suggested are wrong, it just might trigger a light bulb.
Isolate the upper and lower connections, I assume you have valves.
Crack the flanges so both Upper and Lower are reading atmospheric pressure.
The transmitter will now be reading a negative pressure, this is the pressure caused by the column of capillary fill fluid, (Height by SG)
For example 110" x 0.93 = 102.3" WC (for DC 200)
This is also your zero value a Negative No
Your span is Height x SG or 110 x 1.51 = 166.1" WC
So the instrument calibration would be -102.3 to +63.8" WC
BTW I doubt you are using a 12 foot capillary on flanges 12 feet apart, you need to verify the nozzle spacing from a drawing or an actual measurement. Even then sometimes this is not the operating range, the upper nozzle could be above the overflow, the lower nozzle below the pump suction, study the tank drawing, review the range of the other transmitter, is it using the lower nozzle height as zero?
DP transmitters with remote diaphragm seals are expensive and bothersome, where you have a nitrogen purge it can eliminate the need for the remote seal.