PLUS+1 Software > Code sharing

Signal to programmable tachometer.

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PWM output could be a solution for this.

As to the timer / delay firing a digout, this could function for your purposes.  The only drawback would be the accuracy / repeatability needed.  You would be limited to the scan time of the processor being the smallest change of state delay (similar to the digin not being able to 'respond' fast enough).  It is actually not the Input or the Output physically that is the issue but the delay of the updated processor's IO table and CPU logic scan.

Mike AA:
I was thinking this might be an issue when I was looking at the port speeds and only MFP have faster access. Unfortunately I am using all 10 outputs to control 6 hydrostats. I will need to see if one only needs to go forward then I can steal the other half to feed the tachometer.

Thanks for the responses!


Mike AA:
I am back in a situation where I am trying to get this to work. I have a programmable tach and a counter hooked up to C1P46 of an MC050-018. I am reading signal from a motor spinning at upto 300 RPM with 30 pulses per revolution. I am able to read the speed reliably through an IO module to our display. Some of the guys would really like to have the counter and the tachometer showing the readout also.

The counter and tach both look for simply the pulses from a speed sensor (square wave). I setup a oscillator with a true and an on time of 1 ms and a period of 2ms. This should in theory give me 500 pulses per second and both my tach and counter should show 500. The tach is bouncing errractially which I am not worried about. The counter is showing me about 42 pulses, much less than I expected. This seems to be showing me that the port still cant handle the speed. The counter is capable of 10KHZ and when direct wired works fine but we are trying to get away from a mass of wires leading to an area where we already have the IO module and just power and data.

Any other ideas? I was thinking about getting a voltage to frequency circuit but I would really like to get this figured out with software on the MC.


Mike AA:
I made some progress after thinking about how the outputs on the upper level pins are. I have a value of 10 constant connected to the output value of C1P45. I am using C1P24 as a frequency input just monitoring frequency and the two pins connected and then a lead connecting to my counter/rate meter. When I change the Group 2 ReqFreq in the outputs page my counter rate matches and C1P24 matches. I then went into the Group 2, disconnected the ReqFreq pin and put a SET in my program so I can manually change the value for the one pin instead of all 4. Here is where things no longer make sense. Once the program is loaded the ReqFreq apparently got a phantom number that matches the ReqFreq of the other 3 pins that are still connected. In a parameter page I try to set that value and it doesn't change.

Are outputs settings values only set at the beginning on power up or can I simply not split the pin off out of the group?

Mike AAlderink

Mike, can you check what your cycle/scan time is on your MC050?  If your cycle time is, for example, 10ms then your 2ms logical oscillator isn't going to function the way that you want.  My recommendation is, if possible, to scale down your oscillator speed to something that the controller can calculate and make up for that in scaling your tach/counter display.  For example, make your oscillator 10 times slower in the MC050 and in the tach/counter display change the scaling accordingly.


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