Step 7 timer less than 1MS

9Hammy9

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Aug 2019
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Loughborough
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Hello|

I have Step 7 1200 and using a timer to operate a relay, currently the relay remains closed for 1MS.

I need the relay to close for only 0.13MS. I get an error whenever I put a value less than 1MS.

Can anyone kindly tell me how can I have a time for only 0.13MS?

Thanks

1MS.png
 
Is this a solid state relay or mechanical? Asking because most mechanical relays won't be anywhere near that fast, and some SSRs may not either.
 
Timers are not really 'timers'. They are delays of the amount you specify plus the time it takes to get around to processing the 'timer' block. 'Timers' will lose time.
If you want to be more precise then use a system clock with sub millisecond resolution.

Interrupts would be better because they don't lose time but that doesn't mean interrupts happen at regular intervals. The interrupts may be off when it is time for an interrupt so the interrupt will be delayed until interrupts are turned back on.
 
The typical DC relay operates in the 10 ms region. Same goes for SSR relays and contactors.
The regular 24V outputs on an S7-1200 operates within 50 µs to turn on and 200 µs to turn off, but how the make the program actually do that ?
As like others have said, the S7-1200 do not have timers for less than 1 ms. You can add a cyclic interrupts with OB35, but the lowest time setting is 1 ms.

And what is it that must be turned on for 0.13 ms ?
Tell us more about your application, and we can help you better.
 
Maxkling said:
Does your relay and output have that tight of a resolution?
Click to expand...
Sorry for my later reply, I was out on the road since my post.

I only need the contact points of the relay to close for a period of 0.13ms. I am assuming that current would need to flow through the coil of the relay for a slightly longer period than that.


The relay is hard wired to the pcb taken from a QUERTY keyboard. When the relay closes, it triggers an ASCII code out via the USB of the pcb, which in turn is connected to a laptop with a software that responds to the said code and does what it is mapped to do when it gets this ASCII code. So in fact the relay does what a human finger does when it presses on a certain QUERTY keyboard.

This setup was done to make the plc run (in a hard-wired way) a software installed on a laptop. The two systems are only connected by a small pcb of querty keybaord .
 
Peter Nachtwey said:
Timers are not really 'timers'. They are delays of the amount you specify plus the time it takes to get around to processing the 'timer' block. 'Timers' will lose time.
If you want to be more precise then use a system clock with sub millisecond resolution.

Interrupts would be better because they don't lose time but that doesn't mean interrupts happen at regular intervals. The interrupts may be off when it is time for an interrupt so the interrupt will be delayed until interrupts are turned back on.
Click to expand...
Thanks
 
janner_10 said:
I don't think you have a cat in hells chance with achieving that with that plc.
Click to expand...
When the relay closes, I get ACII code for 'space' key . As if you've pressed the space bar on a querty keyboard. But because the duration is too long, I get around 16 spaces instead of just one.
I might have to consider writing a script to block all but the first 'space' character for long enough period.
 
JesperMP said:
The typical DC relay operates in the 10 ms region. Same goes for SSR relays and contactors.
The regular 24V outputs on an S7-1200 operates within 50 µs to turn on and 200 µs to turn off, but how the make the program actually do that ?
As like others have said, the S7-1200 do not have timers for less than 1 ms. You can add a cyclic interrupts with OB35, but the lowest time setting is 1 ms.

And what is it that must be turned on for 0.13 ms ?
Tell us more about your application, and we can help you better.
Click to expand...
The relay is hard wired to the pcb taken from a QUERTY keyboard. When the relay closes, it triggers an ASCII code out via the USB of the pcb, which in turn is connected to a laptop with a software that responds to the said code and does what it is mapped to do when it gets this ASCII code. So in fact the relay does what a human finger does when it presses on a certain QUERTY keyboard.

This setup was done to make the plc run (in a hard-wired way) a software installed on a laptop. The two systems are only connected together by a pcb of a querty keybaord .


Thanks
 

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