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JDHammond1

Need some help! Programming issue!

8 posts in this topic

I have been out of the game of PLC's for going on four years and I have a project im working on. I got 99% of the programming done but im having one issue. I'm doing a probe cleaning sequence with a timer. One way is from our DCS and another is from the operator. I have everything the way I need it when the DCS calls for it. All it is, is a probe going out (air solenoid on) latch bit, probe clean (water solenoid on) latch bit, 30 seconds later, (water solenoid off) unlatch bit and (air soenoid off)unlatch bit. That works fine. My problem is when the operator pushes a maintained button for the manual cleaning it does all the steps except the last. It isnt untill the maintained button is pulled out that the air solenoid turns off. Right now I have the maintained input NC, after the accumulator and it holds it out for the last step, but as I turn the input off, I loose my timer and then the unlatch does work due to them in series. I know this is easy but, i cant seem to figure it out. Please help Thanks,

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Can you post your program? If the section in question is short you may be able to post a readable PDF of it. Otherwize 'zip' your program and post that.

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Seems to me that maybe you need a momentary PB on the HMI. Sounds like the latching of the toggle is holding you up. Or change you code to one shot the PB and then have the end of the sequence unlatch the PB

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something like this perhaps.. of course you can make both inputs one shots (something for you to do, no free lunch ). done properly that would prevent one of signals blocking other (for example maintenance pb left on). Clean.pdf

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It will be the top portion of the program. The bottom will be the same in the end. FERM PROBE FLUSH.RSS

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This is what operations wants I thought it would be best if I tried to document what we decided yesterday. 1) Under normal circumstances, the D3 will initiate the automatic flush sequence. It will do this based on a time interval entered by the technician. (Presumably about 15 minutes). It will flush both the A probe and the B probe, but never at the same time. It will only initiate automatic flushes while the Fermenter is in either the ‘inoculating’ or ‘Fermenting’ state. The technician will be able put the flushes into either ‘Auto’ or ‘Manual’. When in ‘Manual’, he can start a flush by pushing a button. When in ‘Auto’, the D3 will initiate flushes based on time. If a probe is manually flushed and then put back into ‘Auto’, the time resets and it is 15 minutes before the D3 automatically initiates another flush. 2) When the D3 is ready to initiate a flush (either Manual or Automatic), it will first store the current value of the pH probe reading and put the probe in hold for a set period of time (Presumably about 60 seconds). Once the reading is fixed, it will then send a pulse signal to the PLC to initiate the flush. (We have two cables going to the PLC, a pulse on the first cable flushes the A probe, a pulse on the 2nd cable flushes the B probe. 3) When the PLC receives a pulse signal to flush, it will send a 24V signal to the air solenoid valve (on the appropriate probe) to switch positions. This will switch the air supply on the flushable housing and cause the probe to retract. After about 5 seconds, the PLC will send a second signal to the Broth Condensate solenoid valve (again, on the appropriate probe) to open, which will start supplying broth condensate to the tip of the probe. After about 30 seconds, the PLC will reverse the signal to the Broth Condensate solenoid valve, thus causing it to close. 5 seconds after this, it will reverse the signal to the Air Solenoid valve, switching the air supply on the flushable housing back to its original configuration and causing the probe to reinsert. The flush is now complete! 4) For maintenance purposes, each probe will be provided with a local disconnect switch (a toggle of some sort). When this disconnect is pushed, the PLC will send a signal to the air solenoid valve (on the appropriate probe) to switch positions. This will switch the air supply on the flushable housing and cause the probe to retract. After about 3 seconds, the PLC will send a second signal to the Broth Condensate solenoid valve (again, on the appropriate probe) to open, which will start supplying broth condensate to the tip of the probe. After about 30 seconds, the PLC will reverse the signal to the Broth Condensate solenoid valve, thus causing it to close. Note that these steps are identical to those of a normal flush. However, at this point, the PLC goes into hold, AND DOES NOT SIGNAL FOR THE PROBE TO BE REINSERTED. The air lines to/from the retractable housing will all be fitted with block valves, as will the Broth Condensate lines to each housing. If the probes require a calibration (or any sort of maintenance), these block valves should be closed after the probe is retracted and flushed. Once the calibration or maintenance is complete, the block valves are opened up and the toggle switch is reversed – this will cause the probe to reinsert. (Note that we’re leaving it up to the Technicians to insure that the other probe is on control before they do a calibration or maintenance on a probe. This is the same risk that we have today.) Sorry for the length of this message, but I was trying to be complete. Please let me know if I missed anything.

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They both do the same thing except when the operator wants to clean or calibrate the probe he can push the maintained button and it goes through all the steps except the last (go in), until they are done with the probe, then release the maintained button and the probe goes back in.

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Thank you for your help. I was able to go off what you had to make it work! Thanks again!!!

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