I have completed an install of a Rosemount 3051 DP XmTr on an oil & water separator vessel.
this is a flange (high) type DP with the (low) tubed in from the top of the boot. I've researched the SG for this model (.93) and I have measured the distance between the top tap vs. the low tap which is 40". I'm trying to write my LRV and URV, but every time I do the XMTR
my math is :
40"*.86 (oil SG) - 40"*.93 (XMTR SG) = 2.8 LRV
40"*1 (H2O SG) - 40"*.93 (XMTR SG) = 2.8 URV
what am I missing?
I am using a Fluke 709H to calibrate

 

Sketch out your layout and Check your math...
40"*[0.86 (oil SG) - 0.93 (XMTR SG)]= ?
40"[1.0 (H2O SG) - 0.93 (XMTR SG) ]= ?

 

It's -2.8 lrv
4.6 URV
But the XMTR is now showing saturated current

 

what am I missing?
The negative sign on the LRV; you are subtracting a larger number from a smaller number, with a negative result.

For those who haven't a clue what this is about, this is an "interface" application where the desired level is the interface level between oil (SG 0.86) and water (SG1.0), using remote seals on a DP pressure transmitter where the capillary fill fluid has a Specific Gravity of 0.93.

The LRV and URV calculation is shown below.



LRV = Pmin = (0.86 minus 0.93) * 40 inches = -2.8 inches w.c.; LRV = 4.00mA
URV = Pmax = (1.00 minus 0.93) * 40 inches = 2.8 inchs w.c.; URV = 20.00mA