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Glitch counters and PCM

Old 03-08-2004, 10:03 PM
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dirtybird
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Default Glitch counters and PCM

Last summer there was a discussion on whether glitch counters would show any error if connected to a PCM system.
I just completed a test to determine if the glitch counter would show an error.
I used a VEXA Servo Xciter as the tester. This test instument, when plugged into a servo channel, will show the pulse width to a resolution of 1 usec and will also register a glitch when the expected pulse does not appear.
I plugged it into the aileron channel of my Futaba PCM receiver and energised the system. The pulse width measured 1.520 millisec.
I turned off the transmitter. The pulse width continued to masure 1.520 millisec. I switched to the glitch counter, turned on the transmitter and reset the glitch counter to 0 and then turned off the transmitter. The glitch counter continued to read 0.
I repeated the test using a PPM receiver. When I turned off the transmitter the pulse reading disappeared and the glitch counter counted up to 99 very quickly.
Conclusion:
A glitch counter is useless when used with a PCM receiver
Old 03-09-2004, 07:01 AM
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Geistware
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Default RE: Glitch counters and PCM

Could you do this while range testing the model or with an ungrounded electrical source?
I would enjoy having this information available
Old 03-09-2004, 09:46 AM
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sfaust
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Default RE: Glitch counters and PCM

A glitch counter is only somewhat useful with a PCM receiver if its capable of counting failsafe events, as it won't see an actual glitch. Having an idea that your airplane went into failsafe a few times while in the air is more useful than not knowing that happened at all. The glitch counters that I had were able to count failsafe events, and its helped me resolve a problem one of my older airplanes had when the RX went into failsafe multiples times during a flight unnoticed. Also helped on my helicopter when I was having an interference issues.

If its capable of counting glitches on PCM, and failsafe on PCM, they are very useful in both situations. If it just counts glitches, then its of little value on PCM.
Old 03-09-2004, 10:17 AM
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dirtybird
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Default RE: Glitch counters and PCM

ORIGINAL: Geistware

Could you do this while range testing the model or with an ungrounded electrical source?
I would enjoy having this information available
I usually don't range check with a PCM receiver - you have to walk too far. I might get around to it someday. What do you mean by an ungrounded electrical source?
Old 03-09-2004, 10:21 AM
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dirtybird
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Default RE: Glitch counters and PCM

ORIGINAL: sfaust

A glitch counter is only somewhat useful with a PCM receiver if its capable of counting failsafe events, as it won't see an actual glitch. Having an idea that your airplane went into failsafe a few times while in the air is more useful than not knowing that happened at all. The glitch counters that I had were able to count failsafe events, and its helped me resolve a problem one of my older airplanes had when the RX went into failsafe multiples times during a flight unnoticed. Also helped on my helicopter when I was having an interference issues.

If its capable of counting glitches on PCM, and failsafe on PCM, they are very useful in both situations. If it just counts glitches, then its of little value on PCM.
How do you count failsafes? My receivers don't have such an output.
I guess you could program one of the aux outputs to go to minimum when in failsafe but then the glitch counter would not work on that.
Old 03-09-2004, 10:56 AM
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Default RE: Glitch counters and PCM

Thats exactly how to count failsafes on PCM receivers, and is how the glitch counter I use works. For PPM it counts glitches in the normal way, but when in PCM mode it would count failsafe events, even very brief ones. The glitch detector sits on any channel that is programmed for failsafe, and can also share that channel autonomously with any other function if need be. For PPM receivers, it can be used or shared on any channel.

Not the best method to count glitches, but that is all PCM offers us. However, if it tells you your airplane went into failsafe for a brief moment that you hadn't noticed, that information is very valuable no matter how it was derived. Manufacturers should, and could easily, put in a way to count glitches, hold, and failsafe events into the receivers. I wish they would consider this, especially on PCM receivers where glitches are more or less masked.
Old 03-09-2004, 12:07 PM
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HarryC
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Default RE: Glitch counters and PCM

Not getting into a PCM/IPD argument, just pointing out that the new Multiplex synthesised IPD Rx apparently have the option to switch off the IPD failsafe when doing a range check. That way you get to see what is really happening without the failsafe masking the breakdown in range or glitches. I agree, it would be much better if the manufacturers would incorporate proper glitch counting of the raw signal as part of the rx, why don't latest Rx have the ability to store data and then talk to PC and give back a pile of data like the FMA DSR claims to ba able to do.
Old 03-09-2004, 07:29 PM
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Default RE: Glitch counters and PCM

If you turn off the transmitter how can you have a reception error? NOTHING IS RECEIVED, think about it for a half second. A PCM glitch counter, means a signal was received but an error check said the data was incomplete, or out of range, so the data was discarded (failsafe event). If you turn the xmitter off no signal is received AT ALL, so no error can be detected because there is no signal to determine the existance of an error or not. To make the test relevant, put a spark gap interference producer (try a piezo lighter) RIGHT next to the transmitter anttenna and click it while it's transmitting, and see what happens. You may have to electricall connect the lighter to the antenna (Putting the metal cap next to it should work) to get the effect, but you'll see it.
Old 03-09-2004, 08:08 PM
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Default RE: Glitch counters and PCM

Lynx,

It depends on whether you are counting PCM failsafe events, or trying to count PPM glitches. You can count failsafe events which denote glitches and/or absence of the transmitter (transmitter turned off). The counter will increase in either case denoting an 'error' one way or the other. This is how the counter I use works, as it will count either occurrence since the receiver will go into failsafe if it receives errors or otherwise looses the transmitter signal.

Either way you are correct that if he is going to test for this, he needs to induce errors and not just turn off his transmitter which won't give him the expected results. The piezo lighter is a good source. I've used a very reliable and noisy light fixture in the shop which produces excellent noise patterns. I have no idea whats going to happen when that thing fails
Old 03-09-2004, 08:57 PM
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dirtybird
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Default RE: Glitch counters and PCM

ORIGINAL: Lynx

If you turn off the transmitter how can you have a reception error? NOTHING IS RECEIVED, think about it for a half second. A PCM glitch counter, means a signal was received but an error check said the data was incomplete, or out of range, so the data was discarded (failsafe event). If you turn the xmitter off no signal is received AT ALL, so no error can be detected because there is no signal to determine the existance of an error or not. To make the test relevant, put a spark gap interference producer (try a piezo lighter) RIGHT next to the transmitter anttenna and click it while it's transmitting, and see what happens. You may have to electricall connect the lighter to the antenna (Putting the metal cap next to it should work) to get the effect, but you'll see it.
Turning off the transmitter proves that the PCM system immediately takes over and supplies a correct pulse if the incoming signal is absent. It would do the same to any signal that does not meet its criteria.
I suggest you try your test and see. I am satisfied you will find the same results.
Old 03-09-2004, 09:01 PM
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dirtybird
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Default RE: Glitch counters and PCM

ORIGINAL: HarryC

Not getting into a PCM/IPD argument, just pointing out that the new Multiplex synthesised IPD Rx apparently have the option to switch off the IPD failsafe when doing a range check. That way you get to see what is really happening without the failsafe masking the breakdown in range or glitches. I agree, it would be much better if the manufacturers would incorporate proper glitch counting of the raw signal as part of the rx, why don't latest Rx have the ability to store data and then talk to PC and give back a pile of data like the FMA DSR claims to ba able to do.
I have an IPD receiver. When was this mod put in? My receiver was purchased in 2001
Old 03-10-2004, 03:30 AM
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HarryC
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Default RE: Glitch counters and PCM

It's the synthesised Rx that have the option (according to the marketing blurb) and they are not in the shops yet, expect approx another 1 - 2 months.

H
Old 03-24-2004, 01:48 AM
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mglavin
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Default RE: Glitch counters and PCM

The IPD RX 12 Synth does in fact have the ability to disable the IPD Failsafe mode on all channels with the push of a button. Straight up PPM modulation, with all its frailties.

We’ve been testing the new RX now in a small model; so far it’s looking good. Next is a larger gas powered model.
Old 04-21-2004, 03:05 AM
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HarryC
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Default RE: Glitch counters and PCM

The Rx with built-in glitch counter that many of you have asked for is here at last, though it counts all errors not just data errors.

http://www.rcuniverse.com/forum/Mult...1742399/tm.htm

H

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