Yocto-4-20mA-Rx: the answer to exotic needs

Yocto-4-20mA-Rx: the answer to exotic needs

Customers regularly ask us whether we don't want, by any chance, to build a module to measure [insert a physical quantity here]. Sometimes, we jump into it, but we sometimes also decline because the resulting module would be too specific. Therefore, we would likely be unable to sell enough modules to amortize the development costs. We thought about the issue, and we think that we have a reasonable solution.

In fact, we have two solutions. They are the Yocto-4-20mA-Rx, a module allowing you to interface sensors with a 4-20mA current loop as output, and the Yocto-0-10V-Rx for sensors with a 0-10V output.

The 4-20mA standard

Relatively unknown to the general public, the 4-20mA standard is widely used in the industry. There is a multitude of sensors working on this principle: telemeters, gas detectors, humidity sensors, pressure sensors, position sensors, etc.. You name it.

The working principle is very simple: the sensor varies its power consumption between 4 and 20mA depending on the value it is measuring. Therefore, to know the measured value, you only need to measure the sensor power consumption. It does give the feel of an obsolete technology in our day and age when everything is digital, but it's smarter than it looks. As the information is transmitted as a current loop (and not a voltage), the quality of the transmission wire has minor impact on the measures. Therefore, it is a robust and precise method. You can even put the sensor very far away from the reading module. Some sensors work up to one kilometer away.

A pressure sensor, a angle sensor, and a distance sensor, all in  4-20mA
A pressure sensor, a angle sensor, and a distance sensor, all in 4-20mA

One small issue: the sensors are often expensive because they are designed for the industrial world, and therefore are resistant to everything.

The Yocto-4-20mA-Rx

The Yocto-4-20mA-Rx module enables you to read the output of these sensors and to transfer it by USB. The module has a 6x2cm board with two inputs, so you can read two inputs simultaneously: this is luxury. Each input also has a third wire, enabling a 23V power supply independent of the measuring loop to power sensors that require more current than is available on the 4-20mA loop. It is also an isolated module: the current loop is electrically isolated from the USB bus.

The Yocto-4-20mA-Rx
The Yocto-4-20mA-Rx

Small luxury, the Yocto-4-20mA-Rx not only provides you with the power consumption of your sensor, it is able to automatically convert it. You only need to configure it by providing the values corresponding to the two bounds 4 and 20mA. No need for you to do anything else. Magic!

Here is a short demo with some 4-20mA sensors.


The Yocto-0-10V-Rx

The Yocto-0-10V-Rx is the twin of the Yocto-4-20mA-Rx. It works in exactly the same way, but with sensors with a 0..10V output. Working on voltage makes it somewhat less precise than the Yocto-4-20mA-Rx because this time, the wire resistance between the sensor and the Yocto-0-10V-Rx has an influence on the measure quality. So, avoid to put the sensors too far away from the module.

The Yocto-0-10V-Rx, differences with the Yocto-4-20mA-Rx are subtle
The Yocto-0-10V-Rx, differences with the Yocto-4-20mA-Rx are subtle

You are now able to interface many new things, have fun.

1 - kagesk Friday,january 17,2014 10H21

where did you buy pressure sensor?

2 - mvuilleu (Yocto-Team)Friday,january 17,2014 10H25

@kagesk: We bought it from Shanghai Cixi Instrument Co.Ltd (www.gnflowmeter.com)

3 - kagesk Saturday,january 25,2014 22H11

share code?

4 - martinm (Yocto-Team)Monday,january 27,2014 7H19

@kagesk: the demo is written in Delphi. No fancy stuff here, it's just text-book programming. Here is the source code anyway:

5 - anjo Tuesday,february 24,2015 13H13

Fantastic!!! Thank you so much for sharing. I am looking for sensors to monitor environmental values such as RH, T. Could you give me an advice where to find such 4-20mA sensors?

Thank you so much!

6 - martinm (Yocto-Team)Tuesday,february 24,2015 13H30

@anjo: Well, here at Yoctopuce, when we need to measure humidity, we use a Yocto-Meteo, but if you need a rugged sensor with a 4-20mA output, I guess there are plenty of them available from many manufacturers, for instance:

Yoctopuce, get your stuff connected.