How to generate variable frequency output in s7-1200

Hi All,

I have an application where I have to change the frequency to be given to a 'frequency to voltage' convertor in the panel. I have read up and found 'Axis motion control block' in the technology objects that is used to control stepper motors, but has a lot of other blocks like velocity etc which I do not need for a simple application like mine.

Pls help how ro generate a variable frequency in s7-1200 PLC.

Thanks,
Smita

hi,I did something like this before and I made asynchronous generator using timers and counters and CPU with transistor output....

What's the range of frequencies you need to generate? The answer depends on your frequencies.

Hello

There are two pulse generators for the S7-1200 PWM & PTO. I've used the PTO generator in the past for stepper and servo applications. For your application it sounds like you want to use rhe PWM generator. You will need DC outputs I dont think the software allows use of relay. Below is a section out of the S7-1200 easy book on pulse width modulation.

Have A Nice Day
Tom

You want to output a frequency and then send that to a frequency to a voltage converter?

Why not skip the converter and output an analog voltage from a standard analog output that is proportional to the frequency?

Thank you all for your suggestions.

However I am not able to use any of them.
My application is that I need to control speed of a drive by varying voltage. The panel has a frequency to voltage convertor where a 2KHZ i/p gives 10 V o/p which corresponds to a 50HZ on the drive. Now I need to maintain this 50HZ on the drive so I need to increase or decrease the frequency I give to the frequency to voltage convertor.

So Jirr - Timers can give me only 1 ms Pulse while I need a 0.25 pulse(2000hz means 0.5ms cycle time means 0.25ms pulse train)

Wolverine - PWM generates a pulse train of fixed cycle time, only duty cycle can be varied.I need to vary cycle time.

TConnolly - I agree the analog o/p voltage would be the best solution but we have not the provision for an analog card in our system.

How can I vary cycle time in S7-1200 ? PTO through Axis Motion control block?

Could you pls suggest.

Thanks,
Smita

Siemens 1200 Pulse output

Smita Taai , he vaacha.

http://www.automation.siemens.com/m...-functions/simatic-s7-1200/Pages/Default.aspx

i have a s7-1200 plc CPU 1214C DC/DC/Rly.
i want to generate a PWM pulse. i did follow the instruction in s7-1200-system-manual but it don't run
Is'nt CPU DC/DC/Rly generate PWM pulse?
please,help me!
THANKS!

First
I have not try it,but You can enable axis and use MC_MoveJog instruction...there You can change frequency (velocity)....
Second
Maybe You can scale analog input of Your drive,so 1V is 50Hz(do not know details...) and use slower frequency output (I used Micromaster 440 and there You can scale analog I.)

Nice day

You can't use Relay output with PWM or PTO. Your cheapest fix would be to add a DC output Signal Board SB1222 (select 5V or 24V version)

I agree with TConnolly. An analog output module (SB) for the S7-1200 only costs about 65€.
Use the module output to control the speed of your drive. it's a cheap and easy solution.