Products > Test Equipment
Some old school instruments showing how it's done (HP 3325A and Fluke 8506a)
joeqsmith:
That being the case, whats all that hype in the manual? I am not understanding that <5ms should yield > 200Hz yet we are seeing 10X slower results.
bdunham7:
It says 'HI 5.0.4' on power up. Is that the firmware version?
SilverSolder:
--- Quote from: joeqsmith on February 07, 2021, 09:08:25 pm ---That being the case, whats all that hype in the manual? I am not understanding that <5ms should yield > 200Hz yet we are seeing 10X slower results.
--- End quote ---
Hmm yes, the spec sheet does mention 500 readings per second at 6.5 digits.
First, can the meter do that internally, before we talk about outputting the results to the outside world?
Each reading is normally synced to the AC mains waveform. The circuitry supports 4 trigger points per mains cycle (that seems a lot - is it not normal to trigger just twice per cycle?). The 4 points mean that each reading has to take 1/4 mains cycle at best, which in a 60Hz country means 4ms (stated in manual) or 4.16ms if you check the math.
You can turn off the line sync mode and let the meter read asynchronously instead (GPIB command T). Here, the meter no longer syncs to the AC waveform and just runs as fast as it can, held back only by its own processing capability. This is where the meter can do a reading in just 2ms (stated in manual... with dc zero, offset, limits, and calibration factors turned off!) which works out to... 500 readings per second, as claimed by Sales!
What the sales department also neglects to mention is that it is a bit of a challenge to get the individual readings out of the instrument at high rates!
We know from the scan advance scope tests that the internal display cannot go any faster than 20Hz, but there is no reason the serial card (and GPIB) shouldn't be able to run significantly faster than 20Hz.
It is actually possible to de-activate the internal display when operating in remote mode (command "D") - perhaps this is the secret for getting the speed up?
So we have three things to try:
1) disable internal display,
2) mains asynchronous readings,
3) binary mode comms
I suspect if all three are in place, we will see rates closer to what Sales & Marketing are saying.
For most purposes, it is probably easier to just let the meter do the averaging internally!
SilverSolder:
--- Quote from: bdunham7 on February 07, 2021, 09:36:12 pm ---It says 'HI 5.0.4' on power up. Is that the firmware version?
--- End quote ---
Yes, and - the evidence so far - indicates that version number starting with 5 means 8505A, starting with 6 means 8506A.
srb1954:
--- Quote from: SilverSolder on February 07, 2021, 02:29:37 pm ---Apparently the 8080A is only a "up to 4MHz" processor, so it is not picky about EPROM speed.
I wonder why Fluke chose a 15.36MHz crystal to run this board... would that not run the CPU at 1.92MHz?
8080A 2.0MHz
8080A-1 3.125MHz
8080A-2 2.67MHz
8080B 4.0MHz
[edit: CPU speed]
--- End quote ---
15.36MHz is a good frequency for generating the baud rate clock for a UART although this doesn't seem to have been used for the 8506A serial interface as this has its own crystal on board.
15.36MHz/100 = 16 x 9600 Baud
Perhaps Fluke just used this crystal frequency because they had a large stock of them they wanted to use up.
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