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. 

These capillary transmitters can be installed anywhere on your vessel. The HP padcell(remote chemical seal) can be installed on the Top tapping or the Bottom. The transmitter itself can be installed below or above the bottom tapping it will only be limited by the length of the capillary. We normally install the transmitter in a place that is easy to access by the technician that needs to do the calibration and repairs afterwards. All this can be done but the normal and standard way to do the installation is to connect the HP padcell to the bottom tapping and the LP padcell to the top tapping on the vessel and then install the transmitter below the bottom tapping somewhere close to the floor level where it is easy to reach. If this happen to be above the bottom tapping that's fine as well.

The second thing that needs to be done is to install flushing rings between the flange of the tapping point on the vessel and the flange of the padcell. These flushing rings must be specially rated for you application since they will form part of the vessel in the future. We normally do the sizing at the same time as for the transmitter needed for the application. There should also be a 1/2" threaded hole on the top and the bottom of the one flushing ring and only one 1/2" threaded hole in the other one, since you will be installing 1/2" straight instrument fittings in both.

If the gasket needed on the tapping of the vessel is RTJ the flushing ring needs to be RTJ as well.(Ask mechanical dept about RTJ's)
These flushing rings can be manufactured by any engineering company out of 316S/S and have a OD about the same size as the vessel flange diameter below the bolts and a ID the same as the ID of the tapping point pipe on the vessel.

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