DP Level Transmitter Range Calculator
Calculate the calibration range of a DP level transmitter for an open tank, dry leg or wet leg installation, including the head of the impulse lines below the tappings. A 5 point calibration table is generated automatically.
Download
- Calculator sheet with a worked example
- How to Use sheet with steps
- 19 built in formulas, no macros
- Yellow input cells, grey results
- Calculation sign off block
- Excel, Google Sheets and LibreOffice
Worked Example
These are the results of the example already filled in the workbook. Replace the yellow cells with your own data.
Calibration points
| Level (%) | Level above HP tap (m) | Applied DP (mbar) | Output (mA) | Reading |
|---|---|---|---|---|
| 0 | 0.000 | −343.23 | 4.00 | |
| 25 | 0.750 | −269.68 | 8.00 | |
| 50 | 1.500 | −196.13 | 12.00 | |
| 75 | 2.250 | −122.58 | 16.00 | |
| 100 | 3.000 | −49.03 | 20.00 |
About this Calculator
Getting LRV and URV wrong is the most common commissioning fault on DP level transmitters, especially with wet legs where both values can be negative. This workbook applies the hydrostatic equation to each side of the transmitter and produces the calibration points directly.
Basis: Hydrostatic pressure P = ρ g h with standard gravity 9.80665 m/s². Heights measured from the HP tapping.
How to use
- Choose the configuration: open tank or dry leg, or wet leg.
- Enter the process density, and the minimum and maximum level measured from the HP (lower) tapping.
- For a wet leg enter the distance between the tappings and the fill fluid density.
- Enter how far the transmitter sits below the HP tap (0 if level with it).
- Use LRV and URV to range the transmitter; apply the DP values in the table during calibration.
Formulas used
- DP = ρp g (h + x) − ρs g (Hs + x) for a wet leg; the second term is 0 for an open tank or dry leg.
- LRV at minimum level, URV at maximum level; span = URV − LRV.
- Positive LRV is zero suppression, negative LRV is zero elevation.
Related tools
Frequently Asked Questions
Why are the LRV and URV negative with a wet leg?
The wet leg on the LP side is taller than the liquid on the HP side for most of the range, so the DP (HP − LP) is negative.
What is zero suppression?
A positive LRV, typically because the transmitter is mounted below the lower tap with liquid filled lines.
Which density should I use?
The density at operating temperature. A change in density changes the reading in proportion.
Learn more on the blog
DP level transmitter calibration: zero suppression and zero elevation
A practical guide on instrumentationblog.in that explains the engineering behind this workbook.
Read Full Article