Hello,

Is the sensor fail if 24V is applied directly to the loop-powered(current loop) sensor terminals? The pressure sensor is 24Vdc, 4-20mA and 2-wire.

Thanks,

 

No, the sensor will not fail.

A 2-wire, loop powered field transmitter will power up and operate, regulating the loop current (in proportion to how it is configured and whatever it senses) when a 24V dc power supply is connected, with the correct polarity.

This is frequenty done on a bench when configuring a 2-wire loop powered device with a pushbuttons (or magnet stylus) and a local display.

HART communications will not work unless 230 Ohms of resistance is added to the loop.

 

No, the sensor will not fail.

A 2-wire, loop powered field transmitter will power up and operate, regulating the loop current (in proportion to how it is configured and whatever it senses) when a 24V dc power supply is connected, with the correct polarity.

This is frequenty done on a bench when configuring a 2-wire loop powered device with a pushbuttons (or magnet stylus) and a local display.

HART communications will not work unless 230 Ohms of resistance is added to the loop.

Thank you for reply

 

Be aware that there is an entire category of 2-wire loop powered devices that constitute a major exception to the use of a 24Vdc-power-supply-on-the-inputs rule: 2-wire, loop powered valve positioners.

Connecting a 24Vdc power supply directly to the (+)/(-) input terminals of a 2-wire loop powered valve positioner will damage the valve positioner because a valve positioner cannot regulate the loop current like a 2-wire field transmitter or sensor can.

A valve positioner uses loop current from a 4-20mA analog output to operate, but a valve positioner cannot regulate the loop current; it is the analog out that drives the valve positioner that regulates the loop current.

Bench testing or bench setup of a 2-wire valve positioner requires the use of a 4-20mA loop simulator or loop calibrator to power the valve positioner and provide an input signal.

 

"Bench testing or bench setup of a 2-wire valve positioner requires the use of a 4-20mA loop simulator or loop calibrator to power the valve positioner and provide an input signal"

In fact it's much easier to test a pressure sensor or any other instrument using a 4-20mA loop calibrated source as you can check calibration at the same time, also to see it handles less than 4mA before ceasing to function.