Current Control

[kamocat]

Originally Posted by EricVanWyk

Marshall -

Something in my head just jostled loose regarding this statement.

The PID loop uses the current sensor as an input and gives duty cycle as an output. Therefore, the style of analysis you were attempting does not work in this situation. Your example becomes:

% on time = scaling_factor * 1 * (40-2.5)

instead of

Amps = 1 * (40A-2.5A)

Did I mis-state something?.
The output I was recording was the voltage across the motor's leads, as reported by the Jaguar. (I have a Fluke 175 I could use instead if the Jaguars just report a calculated value for voltage)

What do you suppose the scaling factor could be? There is no configuration that relates to this, except perhaps "number of brushes".

[dyanoshak]

Something to note:

If using a Black Jaguar, the current measurement accuracy below 8A is typically +/-2A. When trying to drive at lower currents, you might be reading 0A when it is actually 2A. Above 8A the current accuracy improves to +/- 1A. (This info is in the Black Jaguar Datasheet)

The current sense circuit in Black Jaguar is quite accurate in the higher current range. Unfortunately you get the +/- 1A and +/- 2A thing going on in the lower ranges. This is on our list of things that need improvement.

Gray Jaguar is rated at +/- 1A typically. Like Black Jag, it should improve at higher currents.

-David

[kamocat]

Originally Posted by dyanoshak

Something to note:

If using a Black Jaguar, the current measurement accuracy below 8A is typically +/-2A. When trying to drive at lower currents, you might be reading 0A when it is actually 2A. Above 8A the current accuracy improves to +/- 1A. (This info is in the Black Jaguar Datasheet)

The current sense circuit in Black Jaguar is quite accurate in the higher current range. Unfortunately you get the +/- 1A and +/- 2A thing going on in the lower ranges. This is on our list of things that need improvement.

Gray Jaguar is rated at +/- 1A typically. Like Black Jag, it should improve at higher currents.

-David

Thank you!
For some reason I hadn't seen it there before.
I see it also says "measurement resolution: 10 bits". Does this refer to the ADC on the ARM? Is the +/- 1A resolution the accuracy of the sensor itself?

[dyanoshak]

Originally Posted by kamocat

Thank you!
For some reason I hadn't seen it there before.
I see it also says "measurement resolution: 10 bits". Does this refer to the ADC on the ARM? Is the +/- 1A resolution the accuracy of the sensor itself?

Yes, 10 bit ADC.

The +/- 1A is a combination of the sensor's accuracy and what we measured on multiple Jaguars in the lab.

-David