PWM Actuators.

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MercTech20
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Joined: Sat May 13, 2023 6:20 am

PWM Actuators.

Post by MercTech20 »

I know its possible to tell if certain solenoid actuators are working by analyzing the Voltage/current waveforms of it, eg. injectors. But how can the same be done for actuators that work off a PWM signal? If anyone has any methods please let me know.

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Rfmotors1
TwoWaves
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Re: PWM Actuators.

Post by Rfmotors1 »

I use math channel, positive or negative duty cycle applied on voltage waveform channel.
Current by current clamp will look usually OK without any math channel and if you use the right scaling, the current will match (overlay) the voltage math channel accordingly. If let's say the actuator has intermittent open circuit or short, the waveforms will not match as the current drops or rise up while math channel doesn't.
Regards,
Roman

MercTech20
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Posts: 7
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Re: PWM Actuators.

Post by MercTech20 »

Rfmotors1 wrote:
Sun Feb 25, 2024 4:14 pm
I use math channel, positive or negative duty cycle applied on voltage waveform channel.
Current by current clamp will look usually OK without any math channel and if you use the right scaling, the current will match (overlay) the voltage math channel accordingly. If let's say the actuator has intermittent open circuit or short, the waveforms will not match as the current drops or rise up while math channel doesn't.
Regards,
Roman
Thanks for the reply. I do use the duty cycle measurements but what about actuators that are sticking or stuck with no open circuit/shorts?

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Rfmotors1
TwoWaves
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Re: PWM Actuators.

Post by Rfmotors1 »

Hi, I think this is not easy to see and the only way would be to see the current ramp which could look different from correct actuation but this depends on the type of actuator. Lets say the actuator lifting "heavy" needle, there you would see the difference, (some camshaft soelnoid maybe) but an actuator operating small mass will show not much difference if the needle or object in the actuator have moved (vacuum solenoid etc.)
Regards,
Roman

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Grant_Baker
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Re: PWM Actuators.

Post by Grant_Baker »

Some PWM actuators have constant power and the ground is PWM. For example a variable valve timing oil control valve solenoid. Key ON engine OFF you can apply your own constant ground briefly to look for the pintle bump in current waveform and pintle closing in the voltage waveform.

picowight
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Re: PWM Actuators.

Post by picowight »

I have done this a few times to spot a sticking fuel inlet metering valve. This was a 2.0L diesel that would fault intermittently - say once an hour of driving. I could see the fault in the pressure regulator even though it did not actually fault at the time -
I had pages of normal operation like this :
2023-07-08_17-36.png
Then finally !-
2023-07-08_17-39.png
Note that this was a brand new Bosch pump and regulator. It was replaced and fault gone.

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