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What does mean Clock Memory Pulse_Pause Ratio

Created by: Mr_EWA at: 11/14/2014 7:47 PM (6 Replies)

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11/14/2014 7:47 PM	Rate (0)
Mr_EWA Posts: 30 Rating: (3)	What does it mean when we say that clock memory of S7 has pulse_pause ratio of (1:1). May I know with more elaboration? Anyone here?
Mr_EWA Posts: 30 Rating: (3)
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This contribution was helpful to 1 thankful Users grrrrrroooo

11/14/2014 8:04 PM	Rate (0)
William_B Posts: 5225 Rating: (1203)	Green_Scholar What does it mean when we say that clock memory of S7 has pulse_pause ratio of (1:1). May I know with more elaboration? Anyone here? Hi. Linking this question with some hardware would be nice.. See the PULSE stage as the ON state and the PAUSE stage as the OFF state. That means the frequency pulse is ON for 50% of the cycle and OFF for 50% of the cycle. This specification is normally given when speaking of PTO (Pulse Train Output) that supplies a frequency controlled pulse for something like a Servo or Stepper Motor. In some other devices the change in pulse frequency is used instead of an analog signal to supply a setpoint for a device. In the case of a PWM (Pulse Width Modulation) the pulse frequency is fixed but the ratio ON vs OFF is changed. Again this can be used as a setpoint in a device. In electronics you can use this priciple to dim LED lamps. Does this help? Why this question? w
William_B Posts: 5225 Rating: (1203)
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11/17/2014 9:59 AM	Rate (0)
olloy Silver Member Joined: 8/27/2010 Last visit: 4/13/2024 Posts: 417 Rating: (37)	Hi! I think question is about clock memory, not the PWM outputs. Here is what manual says: The clock memory is a memory byte that changes its binary state periodically at a pulse-pause ratio of 1:1. You select which memory byte is used on the CPU when you assign parameters for the clock memory using STEP 7. You can use clock memory bytes in the user program, for example, to activate flashing lights or to trigger periodic activities (for example, measuring an actual value). Each bit of the clock memory byte is assigned a frequency. The following table shows the assignment: Bit of the Clock Bit of the Clock Memory Byte 7 6 5 4 3 2 1 0 Period Duration (s) 2.0 1.6 1.0 0.8 0.5 0.4 0.2 0.1 Frequency (Hz) 0.5 0.625 1 1.25 2 2.5 5 10
	Last edited by: olloy at: 11/17/2014 10:00 AM
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11/17/2014 12:10 PM	Rate (0)
William_B Posts: 5225 Rating: (1203)	olloy I think question is about clock memory, not the PWM outputs. Brilliant point.. thank you for contributing. w
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11/20/2014 10:45 AM	Rate (0)
Mr_EWA Posts: 30 Rating: (3)	olloy Hi! I think question is about clock memory, not the PWM outputs. Here is what manual says: The clock memory is a memory byte that changes its binary state periodically at a pulse-pause ratio of 1:1. You select which memory byte is used on the CPU when you assign parameters for the clock memory using STEP 7. You can use clock memory bytes in the user program, for example, to activate flashing lights or to trigger periodic activities (for example, measuring an actual value). Each bit of the clock memory byte is assigned a frequency. The following table shows the assignment: Bit of the Clock Bit of the Clock Memory Byte 7 6 5 4 3 2 1 0 Period Duration (s) 2.0 1.6 1.0 0.8 0.5 0.4 0.2 0.1 Frequency (Hz) 0.5 0.625 1 1.25 2 2.5 5 10 In case, let say, Bit 7 with 2.0 seconds period duration and 0.5 Hz frequency. Now considering this value how pulse-pause ration (1:1) will work. "Mbit will be OFF for 1 second and ON for another second" am I right??? If yes, I think there will be an error of 1s every time PLC is restarted, when this pulse is used for counting ! Waiting for your reply !
Mr_EWA Posts: 30 Rating: (3)
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11/20/2014 11:03 AM	Rate (1)
William_B Posts: 5225 Rating: (1203)	Green_Scholar In case, let say, Bit 7 with 2.0 seconds period duration and 0.5 Hz frequency. Now considering this value how pulse-pause ration (1:1) will work. "Mbit will be OFF for 1 second and ON for another second" am I right??? If yes, I think there will be an error of 1s every time PLC is restarted, when this pulse is used for counting ! Waiting for your reply ! Hi. You have a valid argument to make. On restart you are going to be a half phase out if you look at the transition off - on. You could however look at on - off transition. The problem is however more complicated than you think. If you are to use the pulses in a counter to use as if a timer: Realise that you can not assure that the process needing a "timer" is in synchronise with the time pulse you are using. Your time measurement may be out by up to (almost) a full pulse. If you do not have any more hardware timers (older PLCs) then you have other options to work with. It all depends on what you want to do and how long you need to measure. Greetings. w
William_B Posts: 5225 Rating: (1203)
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11/21/2014 6:52 AM	Rate (0)
Mr_EWA Posts: 30 Rating: (3)	Thanx... thats what I want to know !
Mr_EWA Posts: 30 Rating: (3)
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This contribution was helpful to 1 thankful Users William_B

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