symmetricom CS4000 cesium standard, CBT life end ? - Page 1
Forum section: electronics / general

author: testpoint1
author_rank: Frequent Contributor
timestamp: January 03, 2024, 01:22:35 pm
content: Hi all,I got a CS4000, this is first time I touch the symmetricom cesium family, the unit can locked, but seems the frequency deviation a little bit high, according its manual, the clock deviation should be 100-200 (SP tube), but the test show is 315, is this CBT aging problem ?

author: 5065AGuru
author_rank: Frequent Contributor
timestamp: January 03, 2024, 10:39:05 pm
content: Thanks for the connector info!I have not worked on that model but if it is locking and looks to be on frequency I'd run an ADEV plot on it out at least 1000 Sec and see if it meets the data sheet specs.If so then I would not worry about the deviation number.Cheers,Corby

author: testpoint1
author_rank: Frequent Contributor
timestamp: January 04, 2024, 02:52:01 pm
content: Quote from: 5065AGuru on January 03, 2024, 10:39:05 pmthank you Corby, from the test, the deviation about 1 milli Hz of 10MHz, seems OK.

author: rubidium
author_rank: Regular Contributor
timestamp: January 07, 2024, 12:29:18 am
content: I see you are running Monitor3. According to discussions I've had several years ago - in the context of a PRS-50 I was refurbishing - with Robert Lutwak (who is the original author of Monitor3), the DAC gain reported in the Gain Servo section is a pretty good indicator of tube health. According to section 6.5 of the user's manual (page 38), the CS4000 appears to have similar gain servo behavior as the PRS-50 - which shouldn't be a surprise. Specifically: "The DAC Gain varies from 1.4 to 256 over the life of the instrument as 256/N, where N is an integer that varies from 180 to 0. ... A minor alarm (0x18) is declared when the DAC Gain reaches 256, which indicates that the CBT is nearing the end of its useful life." Your system showing a DAC Gain of 32 implies N=8, so the tube is well into it's journey from N=180 down to N=0. That suggests that you'll continue to achieve lock for some time to come, but that the diminishing beam current will be reflected in worsening ADEV. As Corby suggested, only a good measurement of ADEV will tell.Jim

author: edpalmer42
author_rank: Super Contributor
timestamp: January 07, 2024, 04:14:03 am
content: Quote from: testpoint1 on January 04, 2024, 02:52:01 pmYou might want to recheck that measurement/calculation. 1 mHz = 1e-10. For a Cesium standard, that's totally broken. It should be more like 10 uHz, i.e. 1e-12.Does the CS4000 include the STEL-1173 chip? It's used in some other Cesium standards that came from Datum/Symmetricom/Micro-whoever such as the FTS-40xx family and the PRS-xx family. If so, it's known to fail over time. Search eevblog for some discussion about it.Ed

author: rubidium
author_rank: Regular Contributor
timestamp: January 08, 2024, 02:19:08 pm
content: Indeed I would check the STEL-1173. Not only is it well known to fail over time, but it can fail in rather insidious ways. Of the 12 output bits, one or more of the bits of lowest significance can fail and still give you lock but with a poor deviation. Check each output pin with a scope - particularly the lowest significant bits - and ensure that you see switching activity on them.

author: testpoint1
author_rank: Frequent Contributor
timestamp: January 10, 2024, 04:39:42 am
content: Quote from: edpalmer42 on January 07, 2024, 04:14:03 amcurrently my reference is a new SRO-100 Rubidium for the test, for my 5065A, test about 0.6 milli Hz of 5MHz. I do not know if use the STEL-1173 chip, the servo board is under the Cesium tube, let me learn the STEL-1173 chip.

author: testpoint1
author_rank: Frequent Contributor
timestamp: January 10, 2024, 04:40:32 am
content: Quote from: rubidium on January 08, 2024, 02:19:08 pmOK, I try to find it.

author: testpoint1
author_rank: Frequent Contributor
timestamp: January 10, 2024, 05:15:11 am
content: there is no STEL-1173, it may use the U33 "ISL5314" to replace its function.

author: bostonman
author_rank: Super Contributor
timestamp: January 31, 2024, 07:04:26 pm
content: The STEL-1173 went obsolete years ago and not used in the CS4000 (or 4310s, PRS4500, etc...).... I probably changed a few hundred of them when I worked there in the older models.From looking at your monitor screen shot, the Zeeman is higher than the main signal and the DAC is at 32. Also, the deviation is way too high, that should be down around 130 - an indication the signal is noisy.Based on the number of hours, looks like it's over ten-years and that probably has a ten-year tube warranty (or maybe twelve).You could try adjusting the gain pot to lower the DAC. if that fails, and you want a better unit, the next step would be to increase tube temperature.Can you post a photo of the label on the tube?