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Big steps in PicoScope demo waveform

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Big steps in PicoScope demo waveform

Postby Tim Stinchcombe » Mon Jun 09, 2003 6:54 pm

Hi,
I'm looking for a means to be able to get hardcopy from a scope (something analogue scopes don't provide easily!), and a software scope such as PicoScope will give me this. The circuits I'm involved with are not particularly demanding bandwidth-wise (analogue music synthesizers), but do tend to use a lot of CD4000 series chips, and one of the things I occasionally need to know is whether the rise/fall times of clock signals etc. are fast enough for the chips. Basically this means they must be no longer than a few microseconds, and so I would need to be able to easily determine if any rise/fall time was inside or outside this criterion. Thus I downloaded the demo and had a look-see. Whilst looking at the edges of the 'dynamic' sample squarewave at various settings I was a little dismayed to discover that it had rise/fall times of several microseconds, but was being displayed as several large steps, of about a microsecond apiece, which just didn't fall in with my expectations. I then saved the data as text and had a look at it - here is an abridged version (dots are where I have deleted data):

Channel A
Time Value
(ns) (mV)
.
-2046 -390
.
-2006 -390
-1986 -146
.
-1008 -146
-988 190
.
-10 190
10 191
30 194
50 196
70 199
90 201
110 204
.

So two big jumps from -390 to -146, then to 190. Sampling speed is clearly not an issue, and neither is apparently resolution. So my questions are:

1. What is the reason for this?

2. What scale/bandwidth/resolution was the data recorded at?

3. For my intended use, 8 bit resolution and 50MS/s, seems like the minimum requirement, would you agree?

4. I'm running Windows XP Home. The demo crashed on me about 5 times in 2 hours (which didn't impress me at all, but it had been suggested to me before-hand that the software was known not to be 100% bug-free) - do you have a regular schedule of software updates to rectify such problems?

Many thanks,
Tim Stinchcombe
Tim Stinchcombe
 

Postby markspencer » Tue Jun 10, 2003 8:26 am

Hi,

The demo software that you downloaded is not ment to be a represention of our hardware, but a means of demonstrating the software. Depending on the product bought would determine the maximum bandwidth, sampling rate, voltage range and resolution.

The minimum requirement for measuring a frequency is twice the sampling rate. To get a true reflection on the signal you wish to measure you should be considering an over sample of about 4 times or more.

I would recommend that you look at our ADC200/50 and ADC200/100 which are our 2 channel, 8 bit ocsilloscopes, both these have a sampling rate of 50Msps on both channels, and the ADC200/100 has a maximum sample rate of 100 Msps when only one channel is in use.

The buffer size for the ADC200/50 is 16000 samples and the ADC200/100 is 32000 samples.

The full specifications for these units can be found here:
http://www.picotech.com/pc_based_oscilloscope.html

We are always maintaining our software and release upgrades at regular intervals.

Best regards,
Regards,

Mark Spencer
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