Flasher Relay

[Steve Cheung 0]

Hi guys, Anyone know, could PLC used in measure the pulse duration lenght of Flasher Relay when it start to turn on and turn to off? The on / off duration is about 0.45second. Could Ladder measure the lenght of of pulse by the Analog input module? We have a project that measure the Turn on Rate and Turn on time of the Flasher Relay (when it's apply with voltage) at Line Manufacturing. Turn On Time is: After 5 cycles of flash, measure three flashing cycle time (second) Turn On Rate is: After 5 cycles of flash, measure three flashing cycle time(second) and current ON time (second). The Machine already have the system with Industrial PC base. We need to take the data from this machine, which have: 1. Analog Input: measure the pulse on / off from the flasher relay 2. Digital I/O. Anyone knows: Can PLC measure the Duration of pulse between on and off using analog Analog Input ? :*-( Some sample of data that show at the CRT Machine as below: TURN ON A DELAY A: 0.45 SECOND (DURATION WHEN PULSE ON) TURN ON A DELAY B: 0.75 SECOND (DURATION WHEN PULSE OFF) TURN ON RATE: 46.1% TURN ON TIME: 84 SECOND Thanks email: stevr_ch@yahoo.com.sg Edited 12 Feb 2004 by Steve Cheung

[JimRowell 1]

Why would you need to use analogue? The flasher is just a relay which is a digital device. Try turning on an input to the plc with the flasher. If the flasher's output voltage is compatible with the plc's inputs then you can go straight into a plc input with it. If its something else, then you could use another relay powered by the flashers output. To find the 'on' time of the flasher, use a retentive timer operated by the input (the one connected to the flasher). When the flasher goes on, the timer will begin timing. When the flasher goes off, you'll need code that disables the whole thing so that it doesn't start over again with the next flasher pulse. Read the value of the timer. It will contain the time of the 'on' period. You can get as fancy as you like. You could average several flashes. You could separately time the on and the off times, etc. I'll leave it all up to your imagination. Jim Rowell Edited 10 Feb 2004 by JimRowell

[Steve Cheung 0]

Hi Jim, Thank you for your information. But, the voltage apply to the flasher is with 3 different voltage 11V, 12.8V, and 15V. That's way the old machine system is using the analog voltage from the Flasher relay directly. I dont know if PLC could measure the duration with precision 0.01second as the result (from the machine display) pulse on is about 0.45second (two digit decimal). Could PLC ladder measure such the value? Thanks a lot Jim

[JimRowell 1]

Okay, Now I understand. You are reaching the limits of things at 10ms but it's still doable. If you use Mitsubishi's fx2n controller with an 8 bit analogue input module, I'd say you would have enough time to do it (without me actually going and checking the specs). If I recall, the 8-bit has a complete turn-around of something like 2 ms. I'm thinking though that if this is for quality control, you might be better off with a PC and a nice custom interface program coupled with an off-the-shelf analogue input card. If you are able to write the control software, cards are available that will samle at up to 500Mhz and beyond. Jim Rowell

[Sergei Troizky 26]

Don't complicate hardware, guys. All the mentioned voltages can be applied directly to PLC inputs. Also, even the cheapest FX1S has one timer with 1ms resolution. Make it free running and use interrupt(s) to measure duration as difference of two values of this timer. Or use a timer interrupt in order to monitor the input. It may be emulated with pulse train from high-speed output wired to high-speed input(s) with interrupt(s) assigned.

[JimRowell 1]

My thoughts too, Sergei. It just depends on how they want it to be set up. That's partly why I suggested the PC route. It actually simplifies the whole affair from a hardware and wiring standpoint and gives very high abilities to boot such as logging, graphs, whatever. The downside is the complexity of the programming if they are not experienced. A 12 volt input should do fine as you say.

[Steve Cheung 0]

Thanks Jim, Sergai I prefer to choose PLC then PC if it can counter the duration of on and off pulse from the Flasher relay. But, I have check with the special relay list of A1SHCPU, it's only have the smaller clock pulse (0.1s) M9030. As I though, if plc have the 0.01s pulse, I will write a ladder logic to measure the input pulse. When it start on, the special relay pulse turn on too, then add the data to a data memori (DM000+DM001=DM001). But, I cannot found the pulse 0.005s at the specal relay list. When the flasher relay is going to test, there is 3 kind voltage that should apply to it (11VDC, 12.8VDC, then 6VDC), could digital input such as A1SX40 24VDC accept the variable voltage an turn on? Edited 13 Feb 2004 by Steve Cheung