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Relay chatter using PicoLog

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Relay chatter using PicoLog

Postby flatlining » Sat May 02, 2009 6:03 pm

Hi,

I wish to log two slowly changing signals, range 0 to 5 volts DC, using my Picoscope 2205.

I have set up PicoLog with Recording set at Real Time Continuous, Sampling at 1 second and Readings per Sample set at Single.

With these settings and Sampling at or greater than 1 second, the logging performs without any problems.

For Sampling set at anything less than 1000ms, the Picoscope relays "chatter" rapidly. If I change from dual to single channel operation, the problems goes away and I can log the single channel perfectly.

Using Picoscope6 software for timebases above 200ms/div, I run into the "noise" problem, which, I understand, is a known problem to yourselves.

What am I doing wrong? Can you assist me?

I have downloaded and used the most recent software.

Thankyou in anticipation of your help.

Ian.
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Postby PeterF » Tue May 05, 2009 10:10 am

Hi,
The 220x series scopes have relays which switch between the high and low voltage ranges on each channel. When running in PicoLog, the input signal is fed through from one input connector to both channel’s A to D converters in parallel to get twice the bandwidth. Then the other input connector is routed through the same pair of A to D converters and so on in a cycle. At any one time, the unused input connector and pre-amplifier chain is set to the highest voltage (lowest gain) condition to avoid injecting cross-talk onto the live channel. If either channel is set to +/-1V or lower, then the gain relay will cycle continuously. The only way to have two channels in use without the relay noise is to have both set to any voltage greater than +/-1V (+/-2V to +/-20V, they can be different). This is inherent in the hardware design and cannot be changed or fixed in software.
Regards,
PeterF.
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Relay chatter with PicoLog

Postby flatlining » Tue May 05, 2009 3:20 pm

Hi,

Thankyou very much for your prompt reply and explanation of the architecture of the 220x 'scope.

I have followed your advice and I have experimented with the gain settings and have had the following results:-

a) With both gain settings at +/-2V DC and above, there is NO chatter for a sample rate of 1 second and above.

b) With both gain settings at +/- 1V DC and below, there is relay chatter at sample rates above and below 1 second.

c) With both channels set at +/-20V DC, there is relay chatter below 1 second sample rate but not above.

The chatter rate increases significantly when set to record.

As my particular 2205 doesn't seem to comply with your description of its expected operation, would it be advisable to return it to Pico for it to be tested? The signals I am most interested in are 0 to 5VDC.

Thankyou,

Ian.
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Postby Robin » Mon May 11, 2009 9:33 am

Hi

Sorry for the delay in replying.

If you think that your unit is faulty, please email your contact details to support@picotech.com and we can arrange for you to return it.

Robin
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