Not getting proper circuit when installing 24 volt DC relay

Thread Starter

Jonplynch

Joined Jan 28, 2012
93
Hi guys

I am installing a control system for a 2 position dosing valve that will be filling powder into two different vats. The valve itself is a 2 position air valve being controlled by 2 24vdc solenoids. What i have done so far is install 2 tuning fork level sensors (link attached below) so that when one hopper is empty the sensor will begin to call the product and turn on the relevant solenoid and fill to the correct hopper and then shut off the solenoid and sensor when the level is reached! I am doing this through the 2 relay outputs on the sensors one output for call signal and the other output which is switching on and off an Omron 24vdc realy which is controlling the solenoids on the 2 way valve.

The problem i am having is that when i bench tested this it worked fine but when i put the Omron relay into the real circuit on the machine the call signal for the fill does not run but when i take the relay back out of the circuit the call signal runs no problem. So my assumption is that the relay is drawing too much from the circuit and wont allow the call signal to run the way it should. As i said the relay is fine and no faults or shorting are occuring, so do i just not have enough power to do what i am trying? Oh and the way the sensor is working is that it has 0 volts DC when the call signal is running and then 24 volts when the tank is full and the level is met. The sensor in place before was a normally closed type too. I'm just not sure why the call signal wont run when i have the relay in the circuit as all other circuit conditions are healthy

link to level sensor

http://ie.rs-online.com/web/p/level...3743D3338362D393537267374613D3033383639353726


link to relay i am using

http://ie.rs-online.com/web/p/non-l...3743D3335332D383837267374613D3033353338383726
 

Thread Starter

Jonplynch

Joined Jan 28, 2012
93
yes Max the relay is switching off as it should when i put my hand on the level sensor to mimmick a full fill which in turn powers down the solenoid on the valve to allow the second solenoid to engergise and move the flap
 

MaxHeadRoom

Joined Jul 18, 2013
22,831
Well if the relay is picking up as it should but not switching either a contact incorrectly connected or a short circuit occurring, just a question of tracing the circuit out logically with a volt meter.
Max.
 

Thread Starter

Jonplynch

Joined Jan 28, 2012
93
i assumed that too but like i said both work fine independently its when i intagrate them together in the circuit that the call stops working and doesnt show any faults. The only other thing i can think off is that the level sensors are going through solid state relays in the panel and through an on delay timer as well. Could it be that the SSR'S are too small to cope with the extra 24volts of input?
 
Last edited:

Thread Starter

Jonplynch

Joined Jan 28, 2012
93
Hi guys

Just to update i am back at the machine today and traced the cabling back (i have no schematics or drawings for this machine at all) and found that the trigger for the level sensors is going back to the input of the PLC (naturally) so am i right in guessing that the way the sensor is set up in the programme is normally closed and that when the level is reached it is giving a 24 volt output which is a problem for me as i want 0 volts when the level is reached so it will turn off my solenoid too. Alas i do not have access to the programme or the software but would it be a matter of getting into the programme and changing the sensor from NC to NO??
 

MaxHeadRoom

Joined Jul 18, 2013
22,831
You should be able to change the external logic, either the sensor itself or the relay contact from N.O. to N.C. for e.g. etc.
Max.
 

Alec_t

Joined Sep 17, 2013
11,999
so am i right in guessing that the way the sensor is set up in the programme is normally closed and that when the level is reached it is giving a 24 volt output which is a problem for me as i want 0 volts when the level is reached so it will turn off my solenoid too
Without documentation we're all guessing. If the logic is the inverse of what you want you should be able to change the connections inside your post #1 sensor to suit. The user manual shows alternative connection arrangements. The post #10 sensor has a NC and a NO output: take your pick.
 

Thread Starter

Jonplynch

Joined Jan 28, 2012
93
The tuning fork sensor that I have works ok as long as I don't integrate the 2 position flap into it as I need no voltage on the flap when the level is full so the other flap can turn on as I am getting 24v when the level is reached and therefore it is holding on side of the flap on at all times hence why I want to use the barrel sensor to give me 0 volts when full and 24 when empty so would this sensor allow me to do this?
 

Alec_t

Joined Sep 17, 2013
11,999
That one seems to be programmable (presumably with the 'programming buttons'?) to make the PNP output either NC or NO, so looks suitable.
 

Thread Starter

Jonplynch

Joined Jan 28, 2012
93
Thanks a lot Alec just one more thing how is the previous set up able to operate then if the sensor only gives 24volts when the level is reached and 0 when the level is empty?
 
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