### Expert’s answer: Set up a differential pressure transmitter for level measurement?

Using a differential pressure transmitter to measure level is a classic solution because it’s fairly simple. You can measure levels in open and closed tanks or create setups like bubblers. However, doing so requires a little attention to the details.

So today, I’ll tell you where you need to pay attention and also explain how to set up a differential pressure transmitter from zero.

### Open tank

In an open tank, you don’t need to connect the low-pressure side of the transmitter to the top of the tank. You can keep it open to the atmosphere. But the high-pressure input should go at the bottom of the tank with a manifold for easy installation and maintenance.

You also need to avoid air bubbles. So when you open the manifold to let the product into the transmitter, you should drain the air inside using the drain or vent.

You can calculate the level using this equation:

Minimum = level at 0% = HP (SGp * H) – LP (SG * H)

Maximum = level at 100% = HP (SGp * H) – LP (SG * H)

• HP = high pressure
• LP = low pressure
• SGp = specific gravity of the process
• H = height

And by using the local display or handheld, you can access the basic setup, then input the values and units found from the calculation.

### Closed tank

For a closed tank, the low-pressure input should go at the top of the tank. You can also have a wet or dry leg. Read more about that here.

To avoid the air bubble issue here, you should drain both sides. If you have a seal pot, then you need to pay attention to its level, because a difference there can cause issues in the measurement.

This equation works for closed tanks:

Minimum = level at 0% =  HP (SGp * H) – LP (SGf * H)

Maximum = level at 100% =  HP (SGp * H) – LP (SGf * H)

• HP = high pressure
• LP = low pressure
• SGp = specific gravity of process
• SGf = specific gravity of fluid
• H = height

You can also have different situations in a closed level measurement. The article mentioned earlier gives a few such scenarios. So as soon as you find the measuring range, then you can repeat the same procedure to set it up. And that should do it. Hope that helps!

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