Stanford Research DS360 calibration failure - Page 1
Forum section: electronics / repair

author: Jwalling
author_rank: Unknown
timestamp: October 27, 2015, 11:44:59 am
content: A friend of mine just sent out a DS360 for calibration at Tektronix. It failed.Oddly enough, a number of the parameters were at the edge of passing, but still within SRS specification, yet Tektronix listed them as FAIL.Some others were a bit on the high side. Even the ones that were passing were at the hairy edge (high)I've attached the calibration report.My questions:1. Why did Tek list the passing parameters as FAIL?2. Did they really attempt a calibration, or did they just run a performance test?3. If there is something wrong, my guess is maybe a resistor may have gone out of tolerance, yet I think a *true* calibration would have compensated, yes?And the longshot:4. Does anyone happen to have schematics? In my past dealings with SRS, they are not helpful at all with parts or service data unless you are the original owner and bought direct from them. In other words, they suck.Thanks.Jay

author: tec5c
author_rank: Frequent Contributor
timestamp: October 27, 2015, 11:59:54 am
content: Quote from: Jwalling on October 27, 2015, 11:44:59 am1. Because the tests didn't meet the standards... I'd be more concerned if Tek. passed it. At what point then would you say enough is enough.2. & 3. A calibration is a comparison between a set/known standard and another piece of equipment. Commonly mistaken for servicing the equipment in order for it to pass the calibration test.

author: ElektronikLabor
author_rank: Regular Contributor
timestamp: October 27, 2015, 12:06:06 pm
content: See:JCGM 200:2008 International vocabulary of metrologyPage 28 §2.39:calibrationoperation that, under specified conditions, in a firststep, establishes a relation between the quantityvalues with measurement uncertainties providedby measurement standards and correspondingindications with associated measurement uncertaintiesand, in a second step,uses this informationto establish a relation for obtaining a measurementresult from an indication.NOTE 1A calibration may be expressed by a statement,calibration function, calibration diagram, calibrationcurve, or calibration table.In some cases, itmayconsist ofan additive or multiplicative correction of the indicationwith associated measurement uncertainty.

author: dom0
author_rank: Super Contributor
timestamp: October 27, 2015, 12:12:27 pm
content: <goes totally off topic>That's an interesting device you have there. Looking at the THD vs frequency graph:Do you see that blip around 1 kHz? Over 20 dB change in distortion back-and-forth in a couple dozen Hz span! Very interesting. I guess they implemented either someverydelicate noise shaping in their DDS or added some additional analog filters for specific frequencies to boost distortion performance at exactly 1.000 kHz. Also look at the distortion peaks at n*1 kHz.They don't mention this explicitly in their specs except for that graph and a small "Anti-distortion filters" block in the block diagram.

author: Jwalling
author_rank: Unknown
timestamp: October 27, 2015, 12:58:07 pm
content: Quote from: tec5c on October 27, 2015, 11:59:54 amI don't understand this. For instance, unbalanced output at 1 kHz, Nominal = 0.400Vrms. The Max is listed at 0.404 and the measured amount is 0.404, yet this fails.Thanks.Jay

author: dom0
author_rank: Super Contributor
timestamp: October 27, 2015, 01:01:28 pm
content: The measured value might be rounded down for the spreadsheet.

author: Macbeth
author_rank: Super Contributor
timestamp: October 27, 2015, 01:29:18 pm
content: Quote from: dom0 on October 27, 2015, 12:12:27 pmAre you thinking what I'm thinking? Some morally bankrupt engineering going on here? Is SRS a division of Bosch?As for OP, you should ask for a calibration with adjustment - then all the columns headed "as left" would hopefully be within specification.

author: tec5c
author_rank: Frequent Contributor
timestamp: October 27, 2015, 01:35:45 pm
content: Or rather if you want a definitive answer, why wouldn't you (your friend) ask the people at Tek who calibrated it why it failed?