Why use 4-20mA and 3-15 psi rather than 0-20mA & 0-15psi

Why we mainly use 4-20 mA current and 3-15 psig pressure and not use from zero to 20 mA or 15 psig?

For 4-20mA devices there is a single loop which is used to provide the signal and power to the device. If the signal was zero then there would be nothing powering the device. 0-4mA is used to power the device.

If you have an offset signal at zero reading it is good for failure mode indication: If the signal is 0 mA or 0 psi then there is fault with the equipment.

For a pneumatic 3-15 psi signal it is difficult to control very low pressures accurately with a simple regulator, plus you have to provide vacuum to allow for calibration and measurement hysteresis & repeatability errors.

Advantages of 4-20 mA vs 0-20 mA

1. Using 2 instead of 3/4 wires reduces cost of wiring
2. Power supply and signal circuit is combined into one
3. Distinguish between zero signal and a fault
4. Zero offset can be adjusted without need for polarity change of signal

Advantages of 3-15 psi vs 0-15 psi

1. Easier to regulate pressure from 3 psi
2. No need to provide vacuum when regulating zero signal at 3 psi
3. Distinguish between zero pneumatic signal and a pressure failure

Related Help Guides

• How to Connect a 4-20mA Current Loop Pressure Transmitter
• Advantages and Disadvantages of using a 4 to 20 mA Signal
• How to get a 10 volt signal from a 4-20mA output pressure sensor
• How do you measure flow rate with a dp cell
• Supply voltage and load resistance considerations for pressure transmitters
• Choosing calibrator 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
• Flow Transmitter 4-20mA Current Output Calculator
• DP Flow Transmitter Output Calculator
• 4-20mA Signal to Measurement Reading Converter
• SqRt Extraction 4-20mA Signal to Measurement Reading Converter
• Temperature Transmitter 4-20mA Current Output Calculator

Related Product Types

• Water Level Transmitters with 4-20mA Output
• SIL 2 Approved Safety Rated Pressure Transmitters
• Vacuum Pressure Transmitters
• Differential Pressure Transmitters

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