How to Zero a Pressure Transmitter – Three and Five Valve Manifolds Operation ~ Learning Instrumentation And Control Engineering Learning Instrumentation And Control Engineering

How to Zero a Pressure Transmitter – Three and Five Valve Manifolds Operation

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I had discussed previously on DP Transmitter Valve Manifolds where I explained how to remove a transmitter from active service using 3 and 5 – Valve manifolds but zeroing a transmitter is slightly different.
Zeroing a transmitter involves bringing the transmitter to zero signal but does not remove the transmitter from service.The most popular transmitter manifolds are either a 3 or 5-Valve manifold and the operations involved in zeroing a transmitter using these manifolds are different.

How to Zero a Transmitter with a 3-Valve Manifold
Each step involved will be illustrated with a diagram. It is important to realize that over-pressure or transmitter damage could occur if the steps are not properly followed:
Under normal operation
in a 3-Valve transmitter manifold, the two block valves B1 and B2 between the process and instrument ports will be open and the equalize valve, E, will be closed as shown below:


To zero a differential pressure transmitter with a 3-Valve manifold, proceed according to the following steps:

Step 1
Close block valve B2, to the low pressure (downstream), LP,  side of the transmitter (DPT) FIRST

Step 2
Open the equalizer valve, E, to equalize the pressure on both sides of the transmitter. The manifold valves are now in the proper configuration for zeroing the transmitter. The transmitter should decrease and read zero signal at this stage. This can be confirmed with an output device or a HART communicator.

Step 3
After Zeroing the transmitter, close the equalizing valve E.

Step 4
Open the block valve B2 on the low pressure side of the transmitter to return the transmitter back to service.

How to Zero a Transmitter using a 5-Valve Manifold
Under normal operation in a 5-Valve transmitter manifold, the two block valves B1 and B2 between the process and instrument ports will be open and the equalizing valves E1, E2 and drain/vent valve D, will be closed as shown below:
To zero a differential transmitter with a 5-Valve manifold, proceed according to the following steps:
Step 1
Close the block valve B2 on the low pressure , LP, (downstream) side of the transmitter

Step 2
Open the equalize valve E1 on the high pressure, HP, (upstream) side of the transmitter. Do not open the low side equalize valve, E2, before the high side equalize valve. Doing so will over-pressure the transmitter.


Step 3
Open the equalize valve E2 on the low pressure (downstream) side of the transmitter. The manifold is now in the proper configuration for zeroing the transmitter. The transmitter signal should decrease and read zero. This can be confirmed with an output device or a HART communicator

Step 4
After zeroing the transmitter, close equalize valve E2 on the low pressure side of the transmitter.

Step 5
Close the equalize valve E1 on the high pressure side
Step 6
Return the transmitter back to service by opening the low side block valve B2