Help with Latching

[hongkongfooey 0]

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.

[forqnc 2]

I'm not familiar with Siemens but latching your output should be easy to do. The following ladder was done with Directsoft but should easily be implemented into a Siemens PLC. In the example, I show X's are inputs and Y are Outputs, you should just need to change them to whatever Siemens references I/O with. Also you mentioned a low level sensor for Tank 2 but what is this for?

[Groo 7]

In your example your not latching. The first network will always have precedence, if that is Off the output is off. The example above is more like latching.

[Ken Moore 23]

I'm not familiar with Siemens ladder either, but if the instruction set has set and reset, you could use that also. tank_1_hi pump solenoid ----] [------------( set )-- tank_2_hi pump solenoid ----] [---------( reset )--

[wnicholson 0]

From observing the code I am not sure you are using the correct instruction. Look at these I have attached: tmp.doc