If you are running a signal cable over a long distance or have a spare current output pressure transmitter, it is possible to convert the output signal to a voltage type to make it compatible with voltage only input devices.
A typical current output is 2 wire 4 to 20 mA which is designed to be connected in a series with the power supply and other components included in the circuit. The pressure transmitter acts as a current source regulating the current at a particular pressure for a range of load impedances as long as there is sufficient supply voltage to power it.
If a load resistor is added to the circuit in series this will cause a voltage drop across the resistor which is directly proportional to the current being generated by the pressure transmitter. The potential of this voltage drop can be easily measured by connecting two voltmeter probes or an analog to digital converter to the circuit on either side of the resistor.
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The voltage output generated by different values of load resistance on 4 to 20mA current loop are as follows:
| Load Resistor (Ω) | Min Volts | Max Volts |
|---|---|---|
| 50 | 0.2 | 1 |
| 100 | 0.4 | 2 |
| 150 | 0.6 | 3 |
| 200 | 0.8 | 4 |
| 250 | 1.0 | 5 |
| 300 | 1.2 | 6 |
| 350 | 1.4 | 7 |
| 400 | 1.6 | 8 |
| 450 | 1.8 | 9 |
| 500 | 2.0 | 10 |
| 550 | 2.2 | 11 |
| 600 | 2.4 | 12 |
| 650 | 2.6 | 13 |
| 700 | 2.8 | 14 |
| 750 | 3.0 | 15 |
| 800 | 3.2 | 16 |
| 850 | 3.4 | 17 |
| 900 | 3.6 | 18 |
| 950 | 3.8 | 19 |
| 1000 | 4.0 | 20 |
Alternatively use this tool to calculate the voltage drop from any 4-20mA current loop signal and load resistor value.
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Related Help Guides
- How to get a 10 volt signal from a 4-20mA output pressure sensor
- How to Connect a 4-20mA Current Loop Pressure Transmitter
- Advantages and Disadvantages of using a 4 to 20 mA Signal
- Why use 4-20mA and 3-15 psi rather than 0-20mA & 0-15psi
- How do you measure flow rate with a dp cell
- Supply voltage and load resistance considerations for pressure transmitters
Related Technical Terms
- 2 Wire
- 4 to 20 mA Current Loop Output Signal
- HART®
- Square Root Extraction
- Stainless Steel Pressure Sensors
- Transmitter
- Turndown Ratio
Related Online Tools
- Pressure Transmitter 4-20mA Current Output Calculator
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