Siemens Ladder Logic Programming Help Needed.

[Lancie1]

Vivi,

Now that you have an external power supply, you DO NOT use the Siemens PLC internal power supply. Instead, connect your new power supply where the "battery" symbols are on your Siemens wiring diagram.

For example, connect your new 24 VDC power supply "-" (minus) terminal to the Siemens S7 PLC terminals 1M and 2M. Then connect your 24 VDC power supply "+" terminal to ALL of your sensors and input switches. You will need to run many "+"wires, or run one "+"wire that jumps from sensor to sensor or switch-to-switch.

Also connect your new power supply "+" to the Siemens S7 PLC terminal L+, and connect power supply "-" to Siemens S7 PLC terminal M.

Because you will have two or more wires connecting to your power supply terminals, you will need a way to split 1 wire into many wires. You can use some "wire nuts" (wiring terminal connector devices) for that purpose.

 

[viviathevan]

can i know what does the 1M and 2M stands for sir. i got it what you said. thank you so much.

Then connect your 24 VDC power supply "+" terminal to ALL of your sensors and input switches.

but there is 2 wires in each. which one i should connect to the positive?

 

[Lancie1]

...but there [are] 2 wires in each. Which one should I connect to the positive?

For a switch, it does not matter which side you connect to positive (both terminals are electrically the same).

For DC sensors, it can matter, but usually if it does, the sensor will be labeled with a "+" and "-". For your home-made PH sensor, it will not matter which side you connect to "+". Do not connect BOTH sides to +, but connnect one side to +24 volts DC, and the other side of the switch or sensor to your PLC Input terminal for that device.

 

[viviathevan]

do i need to change my programming like normally close or normally open for the ph sensor. can u check my programming for me.

 

[Lancie1]

Yes, I can check it. I have posted a corrected copy previously (Post # 52 is the most correct copy), but I will be glad to check it again if you upload your last program.

 

[viviathevan]

can you inbox me ur email. i will email to you

 

[Lancie1]

Yes, check your Private Messages.

 

[Lancie1]

Update on the student Rain Harvester Project:

Dear Sir,

I have constructed the wiring as follows as in the diagram, but there is a BIG ERROR.

When I turn on the power supply, all the inputs and outputs get energized ( all the 3 LED turns ON. Stirrer motor 0N, and all the solenoid valves are in ON), without me PRESSING the SYSTEM ON/OFF BUTTON. Its like the SYSTEM ON/OFF button don't have any function. I am very sad sir. How i can overcome this problem. Do my connections went WRONG?

How I can over come this problem. During the last minute, this is the problem I am facing, Sir.

When I did the online stimulation, I had tested the the devices such as the FLOAT SWITCH AND RAIN SENSOR, and yes they are perfectly showing the changes in the SIEMENS software but .........

The only problem I am facing is when I turn on the power supply, all the I/O gets on. how can I overcome this? Please give me some suggestions.

Ah, the problems of students! Does anyone have any help to offer? (Wiring diagram is attached). Moggie, send me a copy of your wiring diagram and lets compare to make sure there is not a conflict.

 

[Lancie1]

Latest update from Vivia:

I have tested my plc and yes it is working perfectly. I have tested every load WITHOUT RELAY.


I will download the program and tell you all the progress later sir. okay..

This is the second Siemens S7-212. The first one mysteriously quit working (or never worked). Apparently all 6 transistor outputs got burned out! The loads appear to be less that the 0.5 Amp rating of the Siemens PLC outputs, so it is a mystery about what burned out the outputs.

 

[Jeff23spl]

any use of inductive load for resistive rating ?

 

[Lancie1]

Any use of inductive load for resistive rating ?

There probably was. The only communication on the loads is this chart showing the 3 inductive loads (solenoids) with 0.25 Amps running current. There is also a mixer motor (size unknown).

 

[Jeff23spl]

The is there a reverse diode on the solenoids to short the voltage spike when the coil opens ? If not, this could be a good idea...
I would keep leds but replace valves to be interfaced with a small rail din isolated relay...rather replace a 3$ relay than a plc

 

[Lancie1]

Jeff,

No, there are no diodes being used, unfortunately. Vivia does not seem to be very familar with PLC techniques, and Moggie and I have been trying to just get this project past the instructor demostration. . .

Vivia now thinks that the first PLC bought (used apparently) was already burned out. All 6 outputs apparently were shorted out. So far the new replacemnet unit is working well. I have suggested using a relay at least on Output Q0.1 for the Nutrient Solenioid and the Stirrer motor (0.28 Amp motor, 0.25 Amp solenoid).

 

[Jeff23spl]

ok i see...but there should be at least fast acting 0.5amps fuses on each output then...

 

[Lancie1]

From this update this afternoon, it appears that this PlcTalk project can be marked "complete".

Dear sir, good news!

I am SO SO SO HAPPY that my program and PLC is working as desired and fulfilled all my expectations.

Its working perfectly now as the main problem was with the [defective] PLC.

My outputs and inputs are working perfectly well. All your advice and teaching has helped me lots to achieve it.

Thank you so much for spending time with me all this while when I was all alone doing this project. Even though you are from different country, you stayed with me so long and was with me till today.