adccommunitymod (AutomationDirect) asked a question.
Created Date: April 28,2011
Created By: daveinarmstrong
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My CTRIO counter is firing one of it's outputs after the limit switch deactivates. i thought maybe it was the switch bouncing and causing another signal, but this is not the case. i am using shielded cable for the limit switch. i have 2 inputs and 2 outputs and am using quad counter mode 4X and 2 preset tables that count to a preset and then fire the output. the other output went on and off when the machine was on but not running after an employee touched the outside of the machine. Has anyone had this happen? D4-450 PLC D4-CTRIO counter
Created Date: April 28,2011
Created by: primus
Ctrio
Hello
First thing I would check is your inputs using work bench, if using an encoder I 've had the count increment on its own with no movement (bad encoder). Also check your ladder logic for possible cause.
Tom
Created Date: April 29,2011
Created by: daveinarmstrong
The wiring from the encoder is good because output number 2 works ok (i have 2 inputs and 2 outputs and 2 counts). Count number 1 is actually being zero'd without the limit switch activating. so there must be an external signal effecting it. i have the outputs connected to 2 small 24vdc relays and the count seems to be zero'd out when the 24vdc output is deactivated. Would the 24vdc output signal trigger a false input if the wires were too close? there is not much room between the terminals in this CTRIO.
Created Date: April 29,2011
Created by: Bob S BN
Count number 1 is actually being zero'd without the limit switch activating. so there must be an external signal effecting it. i have the outputs connected to 2 small 24vdc relays and the count seems to be zero'd out when the 24vdc output is deactivated. Would the 24vdc output signal trigger a false input if the wires were too close? there is not much room between the terminals in this CTRIO.
Just a thought, do you have diodes across the relay coils to suppress the back EMF when the coil drops out??
Created Date: April 29,2011
Created by: daveinarmstrong
no. i did not have problems with other applications using this setup but i have no experience with the CTRIO. it must be much more sensitive to transients.
Created Date: April 29,2011
Created by: Do-more PE
Every transistor device is susceptible to transients even if the effects are not as easily noticed as in this case.
Each time a coil has power removed the collapsing magnetic field creates a spike of the opposite polarity that the coil was energized with. This spike then travels along the wiring to the component that is most susceptible where the energy is dissipated.
Whenever this happens the component in question degrades. Eventually the component will fail. It's never a question of if the component will fail, but when.
Long story short, you need to protect your components with some sort of suppression on the coil. This could be MOV, diode, RC circuit, or transorb diodes. All coils should be suppressed.
For 24VDC circuits you can put a P6KE47CA transorb diode across each relay, contactor, and solenoid coil to absorb the CEMF transient spike when the relay is de-energized. For 110VAC circuits you can use a P6KE400CA transorb diode.
Created Date: April 29,2011
Created by: daveinarmstrong
Thanks for the tip. I 've got these transorbs on order. I wonder if they will delay the timing of the output signal. as long as it is a consistent delay, it should not be a problem.
Created Date: April 30,2011
Created by: Do-more PE
They should not affect the signal.
See Chapter 3 of the User manual for how to install them.
Created Date: May 05,2011
Created by: daveinarmstrong
Every transistor device is susceptible to transients even if the effects are not as easily noticed as in this case.
Each time a coil has power removed the collapsing magnetic field creates a spike of the opposite polarity that the coil was energized with. This spike then travels along the wiring to the component that is most susceptible where the energy is dissipated.
Whenever this happens the component in question degrades. Eventually the component will fail. It's never a question of if the component will fail, but when.
Long story short, you need to protect your components with some sort of suppression on the coil. This could be MOV, diode, RC circuit, or transorb diodes. All coils should be suppressed.
For 24VDC circuits you can put a P6KE47CA transorb diode across each relay, contactor, and solenoid coil to absorb the CEMF transient spike when the relay is de-energized. For 110VAC circuits you can use a P6KE400CA transorb diode.
Is there a specific polarity to the P6KE47CA transorb diode? i have one across the coil of my relay and the circuit is occasionally firing by itself.
Created Date: April 28,2011
Created by: daveinarmstrong
My CTRIO counter is firing one of it's outputs after the limit switch deactivates. i thought maybe it was the switch bouncing and causing another signal, but this is not the case. i am using shielded cable for the limit switch. i have 2 inputs and 2 outputs and am using quad counter mode 4X and 2 preset tables that count to a preset and then fire the output. the other output went on and off when the machine was on but not running after an employee touched the outside of the machine.
Has anyone had this happen?
D4-450 PLC
D4-CTRIO counter