Ultrasound sensor to PLC

Hi, I'm new to all this PLC stuff and would be grateful of a little help. I'm trying to connect a 4-20mA Ultrasound level sensor to a PLC and then have it switch a horn at one level and then switch a contactor at another higher level. I'm not too sure if this is possible and also if it is possible how would you program the two different levels.
Any help would be welcomed

Mepone,

If would want to receive answers, it's best that you tell everything we need to know. First of all what kind of PLC are you using? Is this PLC alraedy equipted with an analog input card? Has your sensor a passive or an active output?
The only answer I can give you for the moment is, yes it is possible to program this. It's even very simple.

Best Regards

Yes, and it depends

What you are trying to do is very common and easy. You need a PLC with an analog input built in, or as an add-on card, and relay outputs.

In the program, you would look at the value from the analog sensor The 4-20mA would be turned into some sort of integer in a corresponding range, say 0 - 2048, where 0 = 0mA and 2048 = 20mA.

You would then use "greater-than", "less-than" and equals compare commands to set your outputs, based on the calculated value of the integer (0-2048) where it would be at the mA value you want, using this formula :

2048 * (x/20ma) = y

So, if you want the alarm to go on at 10mA

2048 * (10mA/20mA) = y

2048 * (0.5) = y

2048 * 0.5 = 1024

Then, in your ladder, something like "If Register X > 1024 then Output 1 ON"

The value of 2048 that I picked is "out of the blue". The actual maximum value will vary with the card you choose.

More specific detailed questions bring more detailed answers.

Good Luck!

TM

The PLC that I will be using will be a Mitsubushi PLC with an analogue input card. (as this is the type that I am learning on) The sensor is for monitoring river levels and will measure between 0 and 4.5 mtrs switching first at 2.4mtrs then again at 2.8mtrs so it will need to be on all the time.

The logical operation you want is the COMPARE function. It compares one number with another, and then sets bits (contacts) to indicate the result of the comparison. There sould be examples in your manual. For the FX series this is CMP, FNC 10.

Something to consider is that assuming the river is flowing (has ripples etc.) you may want to take an average signal (time weighted ) for these compares. otherwise you may get false readings.

I do have a question in general about ultrasonic sensors. Can an air stream effect the sensor? Wind blowing or compressed air blowing in the sensors range. Between the sensor and the object to be sensed?


Drewcrew6

"I do have a question in general about ultrasonic sensors. Can an air stream effect the sensor? Wind blowing or compressed air blowing in the sensors range. Between the sensor and the object to be sensed?"

Yes, wind can affect the echo, and in a strong wind the echo can be lost. A "stilling well" is often used to prevent this problem, but if the well is too long or narrow echoes off of it can cause false readings. There is usually a angle of the signal that is provided by the sensor, and anything in this cone will cause problems. Another problems can be foam on the water surface. As you indicate, ripples can cause problems, but many sensors have built in averaging for the output.

Top notch ultrasonic sensors can compensate to an extent for these problems, but not eliminate them entirely. Your vendor should have application guidelines that identify the limits. Properly applied ultrasonics can be very accurate and reliable.

Thank you. I thought that was the case and it might help forewarn Mepone.

Drewcrew6

Other method could be hydrostatic pressure measure. It could be more suitable for water level measure.