Analog IN overflow

[Rickard]

PLC: UIS-WCB1

HMI: 10,4"

program: Unilogic 1.25.56

The Idea: We gonna supervise a valve (digital contact). If the valve is OPEN (NC digital contact) we are supervising it with 1 kOhm. If the valve is closed (digital contact open) we are supervising it with 2kOhm. We also want to supervise if the wiring is lost on its way to the valve or if the wiring is short circuit on its way to the valve  this is to make an alarm if the cable is damaged or someone is trying to cut the cable.

 

Problem: First it worked if we simulated open and closed digital contact. We got a value when the contact was open, we got another value when the contact was closed and we also got  a zero-value when we simulated that the cable was lost on its way to the digital contact(removed one wire from analog in).  So far so good, but the problem occurs when we short circuit the cable on its way to the contact and it stalls to overflow (well it should be) but it wont release the overflow state when we reconnect it to the contact. It can now only show overflow status or zero-value if we remove one wire. It cannot show value open or close anymore.

[Ausman]

There's not really enough information here.  It seems that you want to supervise a digital output by reading the output's voltage (through a voltage divider??) and reading that back into an analogue?  Huh? 

It also seems to me that part of your problem is the way things react to faults.  They specifically act that way on purpose.  Short a power supply and it won't reset until a power cycle.  etc etc.

cheers, Aus

[kratmel]

Change analog input for test. Maybe You lost one of them :(.

Please post contact  supervising cirquit diagram.

I found in one of control box diagram with full diagnostic of the sensor contact wires.

R1=1600 Ohm, R2=200 Ohm, R3= 400 Ohm, R4=200 Ohm.  Zener protect  Analog input .

Circuit open, or high voltage present  U input >= 9V, upper wire short to GND U input = 2.6V, bottom wire short to GND U input = 6.5V

Normal contact open U input = 8V. Normal contact close U input = 4.8V.

You can mount R2 and R3 (or R2 and R4) on sensor side and make protection for shorted and cutted cable.

P.S. You must set short delay after signal is changing for correct error evaluation.

P.S.PS. Maybe use 4-20mA analog input is better solution...