Hi guys:
I would need to measure a time very short. We are speaking about 300ms but I need to have a precision of 1 ms. I only get a precision of 10 ms using timers on step 7.
I have installed sensor of optic fibre and the card is a tipical  DIx16.

I don't know if is possble to measure time in base 1ms with Step 7.

Someone Could I help me? maybe there is a function that does this but I don't know. I have programed with normal timer but I only get base time 10ms.

Thank you

JuanferICT

Hi guys:
I would need to measure a time very short. We are speaking about 300ms but I need to have a precision of 1 ms. I only get a precision of 10 ms using timers on step 7.
I have installed sensor of optic fibre and the card is a tipical  DIx16.

I don't know if is possble to measure time in base 1ms with Step 7.

Someone Could I help me? maybe there is a function that does this but I don't know. I have programed with normal timer but I only get base time 10ms.

Thank you

Hello.

• Which engineering software are you using? (specify exact version)
  Step7 V5.x vs Step7 V1x SPx Update x
  
  
• Which device (PLC?) are you using? (part number, firmware version)
  S7-1x00 vs S7-x00 vs ....
  
  
  
• What is the cycle time of your PLC program?
  1ms vs 5ms vs 15ms vs 50ms vs 150ms vs ....
  
  
• Does your program use any time interrupt OBs?
  Which?
  
  
• Is your system able to use IEC Timers?
  
  
• How accurate measurement?
  Nearest 1ms vs 2ms vs 5ms?
  

BR

#dP

JuanferICT

Hi guys:
I would need to measure a time very short. We are speaking about 300ms but I need to have a precision of 1 ms. I only get a precision of 10 ms using timers on step 7.
I have installed sensor of optic fibre and the card is a tipical  DIx16.

I don't know if is possble to measure time in base 1ms with Step 7.

Someone Could I help me? maybe there is a function that does this but I don't know. I have programed with normal timer but I only get base time 10ms.

Thank you

Hello.

• Which engineering software are you using? (specify exact version)
  Step7 V5.x vs Step7 V1x SPx Update x
  
  
• Which device (PLC?) are you using? (part number, firmware version)
  S7-1x00 vs S7-x00 vs ....
  
  
  
• What is the cycle time of your PLC program?
  1ms vs 5ms vs 15ms vs 50ms vs 150ms vs ....
  
  
• Does your program use any time interrupt OBs?
  Which?
  
  
• Is your system able to use IEC Timers?
  
  
• How accurate measurement?
  Nearest 1ms vs 2ms vs 5ms?
  

BR

Which engineering software are you using? (specify exact version)
Step7 V5.5 + SP4

Which device (PLC?) are you using? (part number, firmware version)
S7-300 CPU 314C-2DP 6ES7314-6CF01-0AB0

What is the cycle time of your PLC program?
10ms

Does your program use any time interrupt OBs?
Which? OB82, OB86, OB100, OB121, OB122

Is your system able to use IEC Timers?

I think that yes

How accurate measurement?
Nearest 1ms

Thanks

Hati

To keep it short and simple. With normal Digital inputs you can only get the same update cycle as your PLC cycle time is. To achieve a lower Input scan cycle, you need a HSC input.

 Good day gentleman,

An IEC-Timer or capturing the CPU clock will better the measurement resolution to be 1ms. But the 10ms cycle of the PLC introduces a fault at the start and end of the measurement. Up to 20ms.

Using technology options (HSC) is the best option and highly recommended. Capable hardware (read: expensive) is needed if you do not already have a able CPU.

This is not the only option. The alternative is to make use of interrupt OBs.



(option 1)
If the input in question can be linked to hardware interrupts, that would be helpful. Taking a reading of the CPU clock on positive edge and taking a reading of the CPU clock on negative edge. Combining the timestamps reviles the duration.



(option 2)
More likely the hardware interrupts are not possible. That means a repeated time cycle interrupt is required -> OB30.

Inside OB30 needs to be the code (example).

L PIW0  //read physical inputs
T MW90  //store readings in memory

Then M90.0 will have the state of I0.0 on every call of OB30. OB30 can repeat at 1ms.. though that is not recommended for its influence on the normal cycle of the PLC.

Some logic is needed combined with capturing the CPU clock tick reading. The measurement will be at the worst x2 the selected clock cycle of OB30. Not perfect but viable.



It has been very long ago since I had to code stuff like mentioned above for the S7-300. I will not be able to expand onto more detail.

BR

#dP

 

Hati

To keep it short and simple. With normal Digital inputs you can only get the same update cycle as your PLC cycle time is. To achieve a lower Input scan cycle, you need a HSC input.

 Good day gentleman,

An IEC-Timer or capturing the CPU clock will better the measurement resolution to be 1ms. But the 10ms cycle of the PLC introduces a fault at the start and end of the measurement. Up to 20ms.

Using technology options (HSC) is the best option and highly recommended. Capable hardware (read: expensive) is needed if you do not already have a able CPU.

This is not the only option. The alternative is to make use of interrupt OBs.



(option 1)
If the input in question can be linked to hardware interrupts, that would be helpful. Taking a reading of the CPU clock on positive edge and taking a reading of the CPU clock on negative edge. Combining the timestamps reviles the duration.



(option 2)
More likely the hardware interrupts are not possible. That means a repeated time cycle interrupt is required -> OB30.

Inside OB30 needs to be the code (example).

L PIW0  //read physical inputs
T MW90  //store readings in memory

Then M90.0 will have the state of I0.0 on every call of OB30. OB30 can repeat at 1ms.. though that is not recommended for its influence on the normal cycle of the PLC.

Some logic is needed combined with capturing the CPU clock tick reading. The measurement will be at the worst x2 the selected clock cycle of OB30. Not perfect but viable.



It has been very long ago since I had to code stuff like mentioned above for the S7-300. I will not be able to expand onto more detail.

BR

 #DP: With Step 7 v5.5 and a 314C PLC, there is no IEC timers available.

314C PLC has HSC inputs as a standard in the first input byte if i remember correctly.

Hati

 #DP: With Step 7 v5.5 and a 314C PLC, there is no IEC timers available.

314C PLC has HSC inputs as a standard in the first input byte if i remember correctly.

RE: IEC-Timers

Thank you Mr. Chartier for a complete answer.

RE: HSC inputs

I somehow missed the C in CPU314C. Your idea is viable and the hardware interrupt usage too. The catch is that the topic starter stated the off CPU input card, I think.

It would be best to use on-CPU inputs.

BR

Thank you to everyone, I have bought a card of high speed inputs, with this and the IEC timers I will test if I can do it.

Thanks