hongkongfooey

Heya, It's been a while since I have had to do ladder programming. I need to make a few latches in my siemens 224 plc using step 7. The intent is to turn on a solenoid valve when the first tank is high. As the first tank is pumped out, the 2nd tank fills, and the 1st tank starts emptying into the 2nd tank. I need to keep the solenoid valve active to keep the 1st tank pumping out until the 2nd tank has reached high level. I was hoping to use a latch to accomplish this. Currently the plan is to use 1 high level sensor on each tank and 1 low level sensor on the 2nd tank. For some reason the latch isn't maintaining, so either my code needs fixing or there is something unique to siemens ladder I'm not aware of. Any ideas? Attached is the latch I am trying to get to work. I also tryed including the latch in the same network, with the same results. I.E. as soon as I deactivate my "collect tank level" input my latch goes away instead of staying on until my treat tank level goes high.

I can see how this type of XIC could be used as a Maintenance bit or similar situation. However if you look at this line of code(rung0035) you will see that O:2/5 is a real world output that causes an actuator arm to tilt down. The actuator arm is used several times during the run, and this is the only way that the arm can be actuated, afaik. Also 15:0/5 is located in almost all of the movement output rungs so it is integral to the operation of the program. I looked through the bit usage files as Ron suggested, but I did not see any FW usage for bit 15:0/5. Or any other word, or file usage for it. There is a touch screen operator interface however, but shouldn't I be able to see the "energizing" function from the interface panel located in the code? I guess what I am going to have to do is, hook up my laptop to see when and how this bit is "energized". Thanks for the help,

I am debugging someone elses ladder code to learn how the system is supposed to run. I haven't been doing ladder for very long, and i have a question about something. What is the purpose of having an internal binary bit that doesn't have any way to either latch it(OTL) or energize it (OTE)? I have attached an example from the code I am working on, as an example of what I am talking about. You can see that B15:0/5 has no way to latch or energize it. How does it toggle? (BTW thanks to Ron Beufort for the "how to" attach files)

Thanks Ron, I knew it had to be that easy. The only change I had to make was adding another NO contact to the compare rung. This makes sure that I won't be watching any TC's I don't want to. AS follows: TC1-Compare...........TC1 ENABLE............TC1_AT_TEMP -----I>=I-------------------I I---------------------( ) ......2500 How do you attach .html files like the one you attached? It's a lot better than trying to create ladder rungs in text format. Thanks for the tip. Chris

Thanks for the response Ron, I am using a Siemens S7-224, with EM 231 thermocouple modules, and a touch panel. The code I posted earlier was a shortened version. The following is what I have: TC1STRT through TC6STRT are the touch screen enable buttons. The TC1 is the compare instruction. As you can see, if I follow this stream of code to the end I will have many, many rungs of ladder. As I will have to code every possible case of enables, and TC compares from TC1 to TC6. TC1STRT..TC2STRT.TC3STRT.TC4STRT.TC5STRT.TC6STRT...TC1 I I----------I/I---------I/I---------I/I----------I/I------I/I--------I>=I----TIMER--REDLT .......................................................................................2500 ETC.. ETC.. Through TC1STRT.TC2STRT.TC3STRT.TC4STRT.TC5STRT.TC6STRT..TC1....TC2....TC3 I I-----------I I--------I I---------I I---------I I----------I I-----I>=I--I>=I--I>=I---- ......................................................................................2500...2500..2500 ....TC4...TC5.....TC6 --I>=I--I>=I---I>=I----TIMER---REDLT ..2500..2500...2500 The basic premise is, to monitor selected TC's from 1 to 6 with any combination thereof. The TC will be selected from a touch screen panel, talking to the plc via profibus. Once all of the selected TC's reach the desired temp (for example 250 deg F) a 1 hour timer is initiated. After the 1 hour timer is complete an output to a red light will initiate. Thanks again, Chris