Set the signal type and the range of the instrument, then type any one of the signal, the percent, the real value or the PLC counts. The others fill in. Example: a 4-20 mA level transmitter on a 22 ft tank reads 12 mA at 50%, which is 11 ft.
1. The instrument range
2. Convert
Type in any box. The others update.
Points along the range
| Percent | Signal | Value | Counts |
|---|
The same point in every signal type
Useful for matching a 0-10 V input to a 4-20 mA output, or the other way around.
| Signal type | At this point |
|---|
Loop resistor (mA to volts)
A precision resistor turns a current loop into a voltage. 250 ohms turns 4-20 mA into 1-5 V.
Loop power check
Does the supply have enough voltage at 20 mA?
Tank level to pressure
For a pressure transmitter at the bottom of an open tank. Use this to find the pressure range to set for the tank height.
4-20 mA tank level calculator
A level transmitter reads 4 mA when the tank is empty and 20 mA when it is full. Enter the full height in the Real value at 100% box and the converter shows the level for any current, or the current for any level.
Steps
- Set the full height of the range (22 ft is filled in as an example) and change the unit label if you use inches or meters.
- Type the mA reading, or the level, in the Convert box.
- Check the table for 25, 50 and 75 percent, and use the tank tool to find the pressure range for a pressure transmitter.
Example
In a 22 ft tank, 12 mA is 11 ft (50%), 8 mA is 5.5 ft (25%), and 16 mA is 16.5 ft (75%).
Questions
- How do I get feet from mA?
- Level = (mA - 4) / 16 x full height. At 14 mA in a 22 ft tank that is 10 / 16 x 22 = 13.75 ft.
- Does the tank shape matter?
- Not for level. The signal follows height. Volume depends on the tank shape and is not calculated here.