FELIX takes you to understand how the output signal of the flow meter sensor works

Have you ever wondered why there are multiple flow meter sensor output signals that can be configured on pressure, temperature, humidity or gas sensing instruments used in process or HVAC applications? Most of these products were originally designed to allow sensor manufacturers to better align with the inputs provided by programmable logic controller (PLC) and direct digital controller (DDC) manufacturers, which are used to control automation and HVAC control the process.

I want to focus on two very commonly used output signals and zero out the advantages and/or disadvantages provided by these output signals. Two very common output signals include analog current (usually 4 to 20mA) and analog voltage (usually 0-10V).

The 0-10V analog voltage output is one of the very common output signals in process and HVAC instruments; due to the number of industrial controllers that will accept or input this signal. Installers and maintenance technicians will often comment on the difficulty of signal verification. One can simply connect a voltmeter in series to read the voltage and correlate the reading with the range on the sensor. When using 4-20mA analog current, it will be troublesome to read the corresponding output signal. It is usually necessary to use a precision resistor in combination with a sensor to convert an analog signal to a voltage signal (Ohm’s law), allowing measurement on a voltmeter. Sensors that integrate 0-10V signals are also more susceptible to electrical interference from devices such as motors or relays, resulting in inaccurate output signals, while 4-20mA analog current output can provide higher noise immunity.

Depending on the location of the sensor and controller, when using an analog voltage output, people may see a voltage drop in the output signal due to the increase in resistance in the long cable line. In the analog current output, the current amplitude in the loop is not affected by the wiring voltage drop, because the current output on the negative side of the loop must return to the positive side of the power supply.

When using 4-20mA analog current output, you can detect whether there is a disconnection, because your signal will now become 0mA. There are some additional analog voltage outputs to help solve this problem, such as 1-5V or 2-10V.

Label：Flow meter sensor, Level meter sensor.