Connect humidity sensor to a PLC

el_b · Mar 12, 2009

Hello,

I am writing my thesis for a company and I have to connect a GEFRAN H5000 humidity sensor to a B&R PLC. The information of the sensor says that if you connect it to a TLC555C oscillator, the signal frequency represents the humidity. But is it possible to 'read' frequency's with a plc?

thanks a lot,

I'm rather new in the PLC world

Brecht.

parky · Mar 12, 2009

In a word no. it sounds like the 555 will give out a pulse train dependant on the humidity (voltage of the sensor) I assume this humidity device must give out a voltage of some kind to control the ocillator chip.
Most plc's have analog cards varying from mv, 0-10v 0-20ma, or 4-20ma.
If you could find out what the actual output is then it may be possible to convert it to a 0-10v or 4-20ma signal.

nonuke · Mar 12, 2009

I don´t agree with Parky.
Frequency is the number of pulses over a certain time.
If you have a digital input that can read up to the max frequency, and if you know the frequency for 0% humidity and the frequency for 100% humidity, you can read the humidity with a digital PLC input.
Simens for example as a level transmitter with a frequency output: 3RG6013-3RS00

nonuke · Mar 12, 2009

You can take a look at the Siemens application for the frequency sensor mentioned above.

http://cmsapps.sea.siemens.com/auto...sor Technology/Set3/MAS3 Technical Manual.pdf

parky · Mar 12, 2009

130hz you will need a high speed input or a counter card.
the resolution will not be very good a better solution is a sensor with 4-20ma or 0-10v output

ATU · Mar 12, 2009

The humidity sensor is a variable capacitor

http://www.gefran.com/getfile.aspx?id=949&src=12a20b21-9732-4e92-9702-2f7f6e9164d9_h5000.pdf

Aproximately 460 - 560 PF

I wonder if there might be an alternative way to use that in a circuit without the 555?

RDS · Mar 12, 2009

If you're into building circuits, National LM2917 is a F to V converter that may work for you. see http://www.national.com/mpf/LM/LM2917.html
Using this you can achieve a DC Voltage output suitable for an analog input on your PLC.

leerob · Mar 12, 2009

Just take another sensor that gives you a signal 4-20ma or 0-10V , keep it simple
Johnson Controls has that type of sensor ,or other brands whatever

danw · Mar 12, 2009

Most capacitive sensors are only really good to 1% RH anyhow, so a 130 Hz signal would likely have sufficient resolution to display the reality of RH.

Sure, lots of device will read out to 2 decimal places, but how real is the reading? With RH, not very likely that it's real.

el_b · Mar 16, 2009

thanks a lot guys!
the reason i chose a capacitive sensor, was his reaction time.

My problem has been solved without using a relative humidity sensor (leakage detection).

thanks !

cheers,

Brecht

Connect humidity sensor to a PLC

el_b

Member

parky

Member

nonuke

Member

nonuke

Member

parky

Member

ATU

Member

RDS

Member

leerob

Member

danw

Lifetime Supporting Member

el_b

Member

Similar Topics