PLUS+1 Software > General controls
Dither Amplitude and frequency for EDC valve
Marbek_Elektronik:
Hi FluidPowerTom,
nobody wants to change dither frequency during the running program.
But if you want to do it , it works: I have placed a NV-memory and changed it and it gives the value to the dither frequenc. It was a test.
You choose one time the correct dither frequency for your valve and then don't change it.
I think high frequency pwm is a good solution, because , it is like constant voltage.
Then add a am-modulation (dither) to change the current.
If you use low fequency, I think, it is very critical.
If the valve has another inductivity (tolerances!) the current will be not the same.
I don't think, it is a good way to do this.
You will have 100% dither, if you do it....
FluidPowerTom:
Marbek, I'd done this on a control unit that is being used by our shop for testing valves. We're using one of the old chipset controllers where the outputs are grouped, and the frequency needs to be 4,000 Hz for when they control PVE pilots and 100-200 Hz when they control typical proportional valves or an EDC. It's a somewhat unique situation, but so far it's working.
oiltronic:
--- Quote from: Jpshockster on September 28, 2015, 02:53:39 PM ---What did you do for your Minimum current? Do you have an issue with the cracking current being higher than the drop out current?
For my valve I have found that 440mA is the cracking current regardless of Dither parameters. Once the valve opens I can lower my minimum to 390mA and maintain motion at a slower speed than that 440mA it took to initiate motion.
--- End quote ---
Hey Jpshockster, did you get it all figured out? I thought one of the points of dither was to get rid of that hysteresis, though I haven't actually had a use for dither anywhere yet. If I'm reading it correctly, note #3 of the MC050 API docs states that if .PinConfig is 5 or 8 (dither enabled) then the PWM frequency for all pins in that group is forced to 4000Hz, regardless of the ReqFreq for that group of pins. And I think the Lynde HPV-02 needs either 100Hz PWM or analogue with 35Hz dither.
Did you measure what was being sent to the pump solenoids, or maybe look at the checkpoints for the actual frequency & current?
Krusty:
How are you figuring out what the perfect dither frequency is?
Jpshockster:
--- Quote from: oiltronic on November 13, 2015, 09:35:08 PM ---
--- Quote from: Jpshockster on September 28, 2015, 02:53:39 PM ---What did you do for your Minimum current? Do you have an issue with the cracking current being higher than the drop out current?
For my valve I have found that 440mA is the cracking current regardless of Dither parameters. Once the valve opens I can lower my minimum to 390mA and maintain motion at a slower speed than that 440mA it took to initiate motion.
--- End quote ---
Hey Jpshockster, did you get it all figured out? I thought one of the points of dither was to get rid of that hysteresis, though I haven't actually had a use for dither anywhere yet. If I'm reading it correctly, note #3 of the MC050 API docs states that if .PinConfig is 5 or 8 (dither enabled) then the PWM frequency for all pins in that group is forced to 4000Hz, regardless of the ReqFreq for that group of pins. And I think the Lynde HPV-02 needs either 100Hz PWM or analogue with 35Hz dither.
Did you measure what was being sent to the pump solenoids, or maybe look at the checkpoints for the actual frequency & current?
--- End quote ---
Its been a while since Ive been to the forum but after exhaustive testing and tinkering Ive found that you must always double check what a mechanical engineer is doing with the valving. Im not sure how to best explain this but i will do my best.... The system had a "Small" built in leakage at the neutral position that would return to tank for cooling purposes. Because these are pilot operated the pilot pressures were slightly different and the built in leakage for cooling purposes was causing me all kinds of grief. It was recommended to use the case drain on the wheel motor to return to tank for cooling. this theory was implemented on a completely different platform and I have not had the issues with this method. With this method I have since returned to pin config to 4 and everything is smooth in both directions once you figure out the optimum cracking current and use the Knee profile on the operator input ie: foot pedal to further fine tune the feel of creep mode. hope this helps.
keep in mind I am no hydraulics major so my descriptions may be somewhat simplified as it took two mechanical engineers and two sales reps speaking to their engineers to figure this out. (if you ask a Mechanical engineer, its always the codes fault) LOL programmers can fix anything!
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