I have a query regarding Capillary type pressure transmitters installed at our Urea Plant.

There are two transmitters installed at Carbamate service. Their specifications have been listed below:

(1) Transmitter Model:FOXBORO I41GP-ES1D1P3EA4H-A2

Range: 0-200 kg/cm2

WITH SPECIAL SEAL ACCORDING TO SNAMPROGETTI SPEC. GA-E-60221

Seal length: 131 mm

Operating temperature: 220 Celcius (max)

(2) Transmitter Model: 141GP-ES1D1P2FAAF-AM2

Range: 0-200 kg/cm2

WITH SPECIAL SEAL ACCORDING TO SNAMPROGETTI SPEC. GA-E-60223

Seal length: 95 mm

Operating temperature: 220 Celcius (max)

Following are my queries :

1.Which factors determine the seal length of the Transmitters, because the service, pressure range and operating temperature for both of these transmitters are almost same? So why one transmitter has 131 mm seal length and other has 95 mm seal length?

2. What will happen if I install 95mm seal length transmitter at location where 131 mm seal length transmitter is installed and vice versa?

Please reply to these queries as soon as possible.

Thanks and regards,

 

A remote seal transmitter with filled capillaries is subject to pressure indication error induced and due to changing temperature, because each capillary and seal is a filled, closed system.

I suspect that the difference in length of the capillaries might be an attempt to minimize the temperature induced error by minimizing the capillary length.

David

 

David is correct. The capillary lengths are determined purely by the application and the rule of thumb is to try and keep them as short as possible for the reasons David have already explained. There will be no difference in accuracy if you install a longer or shorter capiliry transmitter in an application, providing you do your calibration correctly.

The calibration is simple enough in your case. Install the transmitter, zero it and add your zero and span values as per the pressure you want to measure.

With longer capillaries you need to add your calibration calculation to what ever the transmitter reads after the installation since it might be to far away from zero to do a zero calibration. Even if you can do a zero calibration, doing a big zero correction is never a good idea so that is why we prefer to do it like this.