Hello. I have a project using a lot of diaphragm seal DP tx to measure level. But i have a lot of query regarding this. Because i nvr do it before. Any experience guy please help to advise me. Thanks

1. Anyone know why usually diaphragm seal transmitter did not have small range like -100 mbar to 100 mbar???

2. Any mounting concern about diaphragm seal transmitter???

3. how we gonna handle those extra long capilary???

4. Any one hear before the distance transmitter mount below H side cannot be more than distance H side tapping point and L side tapping point.

Diaphram seals introduce a mechanical resistance between the fuild being measured and the sensor. This makes measuring small pressures with a seal impractical.

Be aware that remote seals constitute a closed, liquid filled system, which according to Boyle's or Charles' Lawmeans that the pressure of the filled system is directly proportional to the temperature.

The pressure seen by the sensors in the DP body is the combination of the applied process pressure and the pressure induced by temperature of the closed, filled system.

Which means that the filled capillaries are not only pressure conduits, but thermometers reflecting how hot or how cold they are.  

Temperature variations of the capillaries at 100mbar will be reflected in the pressure at the DP cell is likely to be a considerable percentage of the applied process pressure. 

I am uncertain as to what make of devices you have selected but you may wish to concact rosemount as they have a best practice available that will aid in installations!
Some things to ensure you consider
1-always have equal lengths of capillary lines or the device will NOT work! Changes in ambient temperature will result in constant zero shifts!!!
2- attention must be paid to installation of gaskets for bleed rings to ensure no damage is done to diaphrams(valve). Far to often theses are not ordered with bleed rings and this results in a maintenace headache trying to preform calibrations.
3- the longer the capillary lines the slower the responce time so these devices typically will not prwform well in a control loop application unless they have large capillary lines and short runs.
4- I would suggest you consider insullating capillary lines for beter preformance. Care must be taken to ensure that the lines are protected from external temp. sources!! I have had good success with heat tracing lines with selflimiting tracing above ambient temps and insulating the lines!

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