jesper, steve, any1 outthere plz help advice

[rdrast]

Steve (who knows better than I) said dump 6150 to %AQ003 for a 50/50 duty cycle. If 6150 = 50%, I'd assume that 12300 = 100%, in which case your 50 would equal a duty cycle of 0.4%. That might not be enough to even get the PWM generator running.

 

[crying_baby]

reply

hi, thanks rast,

yes, i tried with some different values from the manuals , and since i cant get to display the pwm in oscilloscope, i turn to look at the register of %q0001, it doesnt turns 0 or 1. it only stay at 1.

then, i go check the register status of aq002 (hertz) as well as aq003 (duty cycle_), they r having the values i set them to.

i'll try to put in more other values for experimentting, but, i tried a ondtr with ofdtr, to turn on and off the q0001 (normal output, not pwm ) , yes, i can c the changing from 0 ---> 1 and --->0 and so on , in the %q0001 memory status of the PLC.

did i miss out anithing, ? the pwm is not as straight forward as explained in the manual book, i go try some more values

 

[CaseyK]

MGD for everyone. Forget the Lite stuph, I need real octane booster.

 

[crying_baby]

i calculate every possible values in excel for teh aq3 and test for the various duty cycles now ok .

 

[crying_baby]

it is very odd, i cannot c the %q0001 changing, plz , where i do wrong. plz enlighten me. plz thank u

 

[rdrast]

I seriously doubt you could see it change in the online monitor...

You aren't actually USING %Q1 anywhere in your program as an output, are you?

 

[crying_baby]

thanks rast, the ladder screenie i posted r the 2rungs only i started with. i didnt %q1 in the ladder, only the register %aq002 and aq0003
and then, i try measureing the output at %q0001

i put 00300 into reg %aq0003 (duty cycle) which after calculating gives around 40% duty, with 50hertz, at . i forgot what value i calculated for 50hz in excel , for register %aq0002, its 24110 , if not wrong,

 

[rdrast]

From the GE Manual for that PLC, just try the following sample values:

%AQ2 = 12299
%AQ3 = 4920

Both in decimal.

According to the table in the manual, that should be 100Hz at a 41% duty cycle.

 

[Steve Bailey]

Have you wired 24 VDC + to terminal 'VC', 24 VDC - to terminal 'COM1', and a pulldown resistor between 'VC' and 'COM1'?

With a voltmeter, at 50% duty cycle and 24 VDC supply, you should read around 12 volts at the Q1 terminal. With a scope, you should be able to see the pulse train if you set up the scope properly.

 

[crying_baby]

Have you wired 24 VDC + to terminal 'VC', 24 VDC - to terminal 'COM1', and a pulldown resistor between 'VC' and 'COM1'?

With a voltmeter, at 50% duty cycle and 24 VDC supply, you should read around 12 volts at the Q1 terminal. With a scope, you should be able to see the pulse train if you set up the scope properly.

thnaks steve, i did connect the pulldown resistor, i measured using the oscilloscope, somehow, i m actually shorting out teh q1 output and alas, measuring teh 24vdc which is feeding the vcc of the q1. i removed the pulldown resistor, and connected a probe directly from q1 output, chnaged the register aq2, and aq3, there isnt pwm comes out.

i connceted back teh pulldown, and measure teh q1 output, using cro, somehow, there IS a signal because, i turn the PLC STOP and the RUN, STOP , RUN, there is a change in the oscilloscope,

to further verify the q1 output, i connected a multimeter to q1 and common it to com1, it says, 23.71volts, dc, which is.. just teh vcc i was feeding.. from teh external supply..

help...advice plz enlighted me

 

[Steve Bailey]

You say there is a change in the oscilloscope when you switch the PLC between RUN and STOP. What voltage do you read on the multimeter when you do it? Q1 is a sourcing output, so you should measure 0 volts at the terminal when the PLC is stopped. If you're seeing 24 volts between terminal Q1 and COM1 when the PLC is stopped, you have either wired it incorrectly or the output has failed in the conducting state.

To test the output to find out if it works, try disabling the PWM configuration and just program simple ladder logic to turn the output on and off.

 

[crying_baby]

hey yo all!! i was kept on trying to get the pwm from the PLC, by configuring the i/o and write directly to the memory registers., i skipped teh ladder,

TODAY I LOAD THE PLC's I/O configuration and look at it , i found out that in the past, i did not update teh i/o from teh PC to the PLC!! how stuPid of me.

after doing that, yes, i got the beautiful square wave pwm out, (finally) with duty of 4ms out of T=10ms, i use the value as calculated , thanks

next, my professor told me to cascade the 3plc and obtain 3phase shifted 120DEGREE pwm signal , .

phew,,, at least now, i got something good to submit in my report due next week..

i reli appreciate the advices given, steve, jesper, rast, every1 in this thread ,

Thanks, i learn my lesson now.

never ever giv up