Hp Agilent 34970A precision logging thread - Page 1
Forum section: electronics / general

author: beanflying
author_rank: Super Contributor
timestamp: December 18, 2017, 10:38:31 am
content: Just starting to get mine ready for some Longer term Voltage reference logging and the other for Temperature calibration for a commercial project.So I popped the top on one of them (broke my first 'cal' stickers) No real surprises it is using a socketed Agilent part numbered LM399 of some sort. The thing that was surprising was the placement relative to the cooling fan. My plan was to drop a good RTD near it to monitor the air close to the reference to give a better idea of the meters true drift against the Vref's and or the RTD/Thermocouples on my other project.Given the photos what would be some thoughts on a board to aluminium top foam shroud around the 399 to reduce airflow or assume Agilent know better and leave it swinging in the breeze?I will also be recording Ref temps and the relay board temp as part of the logging. Still playing with thermal control for the refs.Also no real one thread I was able to find on using these loggers still plenty of individual posts so it's own thread might be not a bad idea?

author: HighVoltage
author_rank: Super Contributor
timestamp: December 18, 2017, 03:53:59 pm
content: The older 34970A are as stable as a 34401A DMM (no fan)The newer 34972A are more like the 34410A DMM (annoying fan noise)I have used both for long term measurements of voltage references and have not noticed a need to change the setup or protection of the LM399 reference.It looks like you should clean your fan from dirt.Or is that just a bad picture?

author: beanflying
author_rank: Super Contributor
timestamp: December 18, 2017, 07:30:08 pm
content: It is a little dirt, the last shot I had the flash on so it isn't that bad.Both units came from a Auto electronics manufacturer so fairly clean and about a year out of Cal.

author: ManateeMafia
author_rank: Frequent Contributor
timestamp: December 19, 2017, 04:48:13 am
content: I started using one a few weeks ago to log thermistor readings from my Fluke 732A/B. It will be good to have a long term oven monitor in case something goes wrong with the output.

author: mikeg
author_rank: Newbie
timestamp: December 19, 2017, 05:04:08 pm
content: Used to have 2 of them. I miss this meter.

author: e61_phil
author_rank: Frequent Contributor
timestamp: December 20, 2017, 03:30:03 pm
content: Quote from: HighVoltage on December 18, 2017, 03:53:59 pmMy old HP 34970A has also a fan.Do you have experience with the stability of the 3497xA?And does anyone know if the ADC is the same in the 34970A as in the 34401A? They say 22Bits at many places, but the rest of the specifications looks quite similar to the 34401A.I would like to use the 34970A to measure a couple of shunts, but I'm not sure if it is as reliable as the 34401A.

author: Kleinstein
author_rank: Super Contributor
timestamp: December 20, 2017, 05:04:59 pm
content: HP used the ADC circuit of the 34401 quite a lot, it is not just the 34401, but also the 34420, the 34970 and even some power supplies.The layout can be a little different and possibly other grade parts (resistors), especially in the supplies. So performance can be a little different. Also software could be a little different, though I doubt it. So I won't expect a big difference between the 34401 and the 34970.The shield around the board keeps out much of the direct air flow from the ADC and reference section. So I won't expect so much trouble from the fan. Some slow flow can be even good.

author: HighVoltage
author_rank: Super Contributor
timestamp: December 20, 2017, 09:23:49 pm
content: I have found the 34970A to be very similar to the 34401A in regards to stability.One big limitation of the 34401A was the low level AC voltage and AC current measurements and that was solved in the totally different 34410A DMM. The circuitry of the 34410A made it in to the 34972A and that is why it is so much better for low level AC measurements.

author: beanflying
author_rank: Super Contributor
timestamp: December 21, 2017, 02:18:13 am
content: Just popped the top on my 34401a as I haven't in the past. The two ic's near the ref between it and the inputs are the same and the resistors leading in share a similar layout to the 34970 photos above.