In the world of linear position sensors, analog reigns supreme. Sure there are all kinds of other sensor interface types available: digital start/stop, synchronous serial interface, various flavors of fieldbus, and so on. But linear position sensors with analog outputs still account for probably two-thirds of all linear position sensors sold.
When choosing an analog-output position sensor, your choice generally comes down to analog voltage (e.g., 0…10 V), or analog current (e.g., 4…20 mA). So which should you choose?
0…10V versus 4…20 mA
When it comes to sensor interface signals, 0…10V is like vanilla ice creamr. It’s nothing fancy, but it gets the job done. It’s common, it’s straightforward, it’s easy to troubleshoot, and nearly every industrial controller on the planet will accept a 0…10V sensor signal. However, there are some downsides. All analog signals are susceptible to electrical interference, and a 0…10V signal is certainly no exception. Devices such as motors, relays, and “noisy” power supplies can induce voltages onto signal lines that can degrade the 0…10V sensor signal. Also, a 0…10V signal is susceptible to voltage drops caused by wire resistance, especially over long cable runs.
A 4…20 mA signal, on the other hand, offers increased immunity to both electrical interference and signal loss over long cable runs. And most newer industrial controllers will accept current signals. As an added bonus, a 4…20 mA signal provides inherent error condition detection since the signal, even at its lowest value, is still active. Even at the extreme low end, or “zero” position, the sensor is still providing a 4 mA signal. If the value ever goes to 0 mA, something is wrong. The same can not be said for a 0…10V sensor. Zero volts could mean zero position, or it could mean that your sensor has ceased to function.
In some cases, 4…20 mA sensors can be slightly more costly compared to 0…10V sensors. But the cost difference is becoming smaller as more sensor types incorporate current-output capability.
For more information on linear position sensors, click here.
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Scott Rosenberger
Scott Rosenberger has experience and knowledge of the industrial automation industry with Balluff. With his product and industry knowledge, he is sharing his passion for automation with Automation Insights.
I don’t get how current signal would reduce Electromagnetic interference. Switching of relays will draw current which will create EMI that the analog sensor wire will catch.
Generally, the control input for a voltage signal would be a high impedance input, which is more susceptible to induced noise than a low impedance current input.
I agree. Great/simple explanation.
Reblogged this on mmuenzl.
thank you for this scott
I think this one I copied from other site is a good one as well:
Posted by Jebastin anand on 26 November, 2012 – 12:44 pm
All PLC & DCS controllers having input and output processing signal is 1vdc to 5vdc. so according to the Ohms Law,
V=IR
V=4mA*250 Ohm
V=0.004*250
V=1V
V=IR
V=20mA*250 Ohm
V=0.02*250
V=5V
here,
R=250ohm is constant instrument cable resistance.
so if a have a 4mA signal i can feed it to the 0-10VDC controller just by adding 250 ohm resistance in series to it ?
The resistor would need to placed in parallel, not in series. And a 250 ohm resistor will result in a range of +1V to +5V. A 500 ohm resistor will provide a +1V to +10V output. You will never get 0V to +10V with a 4-20 mA current signal. However, sensors are also available with a current output ranging from 0 to 20 mA, which will provide a 0V to 10V signal.
For more information, https://sensortech.wordpress.com/2012/11/14/e-ir-its-not-just-a-good-idea-its-the-law/
You will have to add resistance of 500 ohm for 4-20mA signal conversion to 0-10V.
It’s very well simply explained for a newbee. Thanks for the explanations.
You should not compare those to measure ranges with that closing argument. You’ve forgot about all the other measure ranges. With for example a 2-10V signal, 2V will mean zero position and 0V will mean error. 0-20mA is also a measure range that will have the same problem as 0-10V.
To be sure, there are other ranges of outputs that are sometimes used. However, since 0-10V and 4-20 mA are by far the most common signal outputs used in industrial automation, those are the one we focused on. But thanks for the feedback.
I knew that, but not to say it so nicely 🙂
Thanks for the well presented info!
very good explanation; I get clear in th infoemation
That sums it up nicely