Latching Output Question

[mchitsab]

Hi,

I am using a pusbutton to latch an output for a solenoid. Another pusbutton is used to unlatch the output. If I latch the ouput then turn the power to the PLC off and on again the output remains latched.

Is there any way I can automatically unlatch an output if power to the PLC is lost.

 

[OkiePC]

What type of PLC is it? If it's A/B, add a branch with XIC S:1/15 to your OTU rung. S:1/15 is only true for the first scan after power up.

 

[mgvol]

Try this.

 

[mchitsab]

Hi OkiePC!

Thanks for the tip. I am using an AB Micrologix 1000 and I used S:1/15 (First Pass) on the OTU rung as you suggested and it worked.

Mahen

 

[tom_stalcup]

I remember someone (maybe Terry?? I've slept since then) saying that they set their programs up with the first scan bit operating a "startup" routine to put the machine into a safe condition before actuating any of the operating plc code.....

 

[RMA]

I remember someone (maybe Terry?? I've slept since then) saying that they set their programs up with the first scan bit operating a "startup" routine to put the machine into a safe condition before actuating any of the operating plc code.....
__________________

This is something I've done for my current project and will probably incorporate in future projects. This project is a high voltage capacitor bank, magnetic field research system, incorporating motor driven switches which can also be manually switched. In order to be on the safe side, after every experimental run, I force the operators to return to a login page, where on login the whole system is set back to a safe state.

 

[BOWRIDER]

If he is using AB and using the otl otu instructions it will power back up in the energized state if it was energized when power was lost, if he set it up as "seal in contacts" it would power back up "de-energized. I believe.

 

[rsdoran]

I am using a pusbutton to latch an output for a solenoid. Another pusbutton is used to unlatch the output. If I latch the ouput then turn the power to the PLC off and on again the output remains latched.

Personally I avoid latch (OTL) and unlatch (OTU) as much as possible. Since you are using 2 pushbuttons why not use one with NC (normally closed contacts) Stop and one with NO (normally open contacts) Start then let the OTE (which is NOT retentive) latch the ckt?

Technically you could use a NO pushbutton and an XIO but I prefer STOP buttons be normally closed. If a NO contact goes bad then how do you STOP the system?

I reckon its personal preference.

 

[TRACY H]

Ok

It may not be as straight forward as you think. Take a look at this
http://www.plctalk.net/qanda/showthread.php?s=&threadid=11035
Be sure to read Ron Beaufort`s Post #939

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