Servo Current logs/displays erroneously - RC Groups
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May 05, 2012, 02:48 AM
Registered User

Servo Current logs/displays erroneously

I've noticed that "Re-zero current sensors" under the Calibration menu does not seem to be of any value for the Servo Current expander, as many other actions rezero the servo current sensor, whether I want it to or not, leading to erroneous "backward" behavior from that point forward.

My set-up is very simple: I'm logging RPM, EGT, CHT, ambient temp, and ignition module current for a gas (spark ignition) engine test stand. I have the latest SW version 10.04 loaded.

My data recorder has it's own separate battery and it has seagull transmitter, EGT expander, and Servo Current expander attached. Servo current sensor is measuring the current out of the ignition module battery. Hall sensor is "y" cabled to data recorder and ignition. Removing the extra ground connection by disconnecting the Hall sensor from the recorder does not change the behavior.

After much testing, I've determined that the Servo Current Sensor must zero every time the recorder is turned on, and from that point forward, records the absolute value of the difference between the live current and the current present when it started. If the current sensor has a load when started (ignition "on" in my case), then the downloaded data from the recorder will show no current, then show positive current when I turn the load off (ignition off). Direction of the connection through the current sensor does not matter. It behaves the same both ways.

In addition, if the USB cable is connected to the computer, the servo current sensor rezeros again. Starting and stopping Live mode zeros again. If I use the dashboard, it also appears to rezero itself separately when it is turned on. So the recorder can be logging erroneously "backward" while the dashboard can be correct or backward depending on if there was load current flowing when I turned on the dashboard receiver.

And finally, it appears that if the dashboard is connected to the computer, it will rezero, if it is disconnected from the computer to run stand-alone it will rezero, and if I start "live mode" using the Dashboard it will rezero again.

Is there a way that the "Calibration" of the zero on the current sensor can be made persistent and prevent the backward behavior? Can each piece of the system simply log/report/display what the calibrated servo current sensor sends to it?

I was also going to use the servo current expander to measure the current of the telemetry system itself, with and without each of the expanders, or with high or low tx power, but this would seem to be impossible. Is this correct?

Also seems that it will require a separate recorder battery to be able to measure the current of a receiver and servos, and even then would require they be turned on in the correct order to account for servo idle current and the rx current. Is this also correct?
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May 09, 2012, 07:33 PM
billpa's Avatar
Hi Clarkson,

The way it is designed to work is that when you click on the "rezero currents" function, the present current reading through the servo current sensor is recorded, and treated as the zero reading for both Seagull Dashboard, logged data, and live mode data display.

We're attempting to reproduce your issue here. I will post again with our findings (we're a little backlogged right now).
May 15, 2012, 12:04 AM
Registered User
Bill, thanks for looking into this. It was suggested to me that measuring the current of the telemetry system itself with the servo current sensor is not impossible, but just requires two batteries; one that powers the system through the current sensor, and a second that powers the system without going through the current sensor. After it all boots and zeros and I've enabled the dash board and live mode and all reads zero, then switch on the battery that goes through the sensor and turn off the first. The batteries must be the same voltage, or I can use one battery through two switches. Switches must be on the negative side since the sensor is measuring the current in the negative lead, or the sensor leads can be moved so the sensor measures the positive side as you've suggested on another thread.
Jun 02, 2012, 08:19 PM
Registered User
Has anyone else had similar issues with the servo current sensor providing unusual results? Anyone else able to duplicate having the displayed current rezero when the dashboard receiver is turned on after the recorder?
Jun 09, 2012, 01:31 PM
billpa's Avatar
Hi Clarkson, sorry for the delay in getting back to you. We have reproduced the issue in-house. It is taking us some time to get it debugged and fixed, due to the heavy spring workload we're experiencing. We should have this addressed soon, though.
Oct 03, 2012, 05:08 PM
Registered User
Any update on this? I'm having the same problems.

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