Data Tech and Weston digital Panel Meter info from the mid 1970's - Page 1
Forum section: electronics / general

author: trobbins
author_rank: Frequent Contributor
timestamp: April 19, 2024, 01:25:56 pm
content: I'm progressing through the restoration of an RFL Industries AC/DC Calibration Standard model 829G from the mid 1970's. Unfortunately this unit is missing its Digital Panel Meter.Luckily the 829G manual was on-line here:https://www.davmar.org/pdf/RFL829G.pdf, and an advert is shown here:https://ieeexplore.ieee.org/stamp/stamp.jsp?arnumber=5213241. But the manual is a little short on details.This equipment either used a Data Tech 344-2, a Data Tech 4212-02, or the Weston Model 2471 DPM. I can't really locate any relevant catalogs or adverts for Data Tech or Weston's ranges of DPM's, or a manual for those specific models. The attached photo of a Data Tech below would be similar, as it uses two separate rear connectors, with one connector related to options. The optional functionality in my missing 4212-02 model appears to include an over-voltage/range signal to then trip the unit; a HOLD signal to retain the displayed value; what appears to be a parallel printer port; decimal point inputs; and a front panel full scale adjustment.From the fault-finding notes, the 4.5 digit meter appears to have a high input impedance and 1.4V max input, which relates directly to an optional Standard Cell used for self-calibration of the equipment's ranges. The 829G manual only makes passing reference to a separately provided DPM manual.If anyone has any manuals etc on these DPM's I'd appreciate a post/PM.The restoration doesn't pedantically need the panel meter, as a modern meter and some simple form of decimal range display, and perhaps an over-voltage detector, should be fine, but always worth chasing up details if they still exist. This calibrator seems to have been mainly sold into the defence force establishments, so perhaps uncommon to see in a cal lab.

author: trobbins
author_rank: Frequent Contributor
timestamp: August 01, 2025, 06:14:55 am
content: Just located a Weston Model 2471/2472 manual athttps://www.surplussales.com/items/115388/weston-digit-display/.Relative to the internal Weston Cell measurement, the 1.9999V FS meter range has a 1,000Megohm input resistance, and uses a LM399H and ICL7103 based ADC, so appears to be the dominant limiting aspect of the calibrator accuracy.I've confirmed that although the meter could provide an over-range control line, the 829G doesn't include a trip interface to use any such line. So the only other function needed from this meter is an isolated +/-12Vdc to power a vintage AD146J opamp, which I can easily work around.Ciao, Tim

author: Poroit
author_rank: Frequent Contributor
timestamp: August 01, 2025, 07:32:41 am
content: G'day Tim,These companies may be able to assist with a replacement.https://www.texmate.com/https://catalog.defineinstruments.com/?product-page=2I have used products from both for past applications.

author: m k
author_rank: Super Contributor
timestamp: August 01, 2025, 01:28:23 pm
content: Peek and poke of 4412-02.Can't be exactly sure what is what.Different column of n.c can be missing component instead of completely missing connection.Color stuff is original wire stumps etc.RC is a filter.J1-H connects to -180V through the resistor.J1-J can't sayJ1-1 connects to the middle of series diodes.

author: trobbins
author_rank: Frequent Contributor
timestamp: August 02, 2025, 08:18:50 am
content: Thanks for info on replacements and similar instruments.My initial aim is to clarify what function and performance the original meter provided. Although I may come across a 4.5 digit meter of similar front face cutout to easily install, its likely that I may only provide 4mm banana terminals and use an external DMM as a practical workaround for display, and that may even be a better outcome if the RFL 829G internal precision resistors (typically +/- 0.01% tolerance CTG-Crestwood) have not drifted.

author: m k
author_rank: Super Contributor
timestamp: August 02, 2025, 07:02:52 pm
content: Old panel meter is modular, faceplate is also an option, sort of.So generally all are generally suited, if range matches, and even that can possibly be easily changed.Can't be sure, but pretty sure that 4212-02, 4312-02 and 4412-02 are generally the same 2V meters.So if you accept that primary transformer's primary is unbalanced you have quite many alternatives.

author: trobbins
author_rank: Frequent Contributor
timestamp: August 06, 2025, 08:11:18 am
content: The RFL 829G calibrator has a 'front end' source that generates a DC or AC output level, and effectively a separate 'back end' that displays the output level being used as the calibration standard. So the panel meter is per se just acting as an accurate display of the chosen output standard. As such, a suitably specced, modern auto-ranging 5-6 digit DMM can simply be used to make the 829G functional again for voltage, and for current with the DMM inserted in the current path. Given the stability of the source, and AC settings of 50, 60, 400 and 1kHz, and the ability for fine adjustment within each decade range setting (0.1V to 1kV, or 0.1mA to 10A), this beast is quite versatile for calibration services, and as accurate as the available DMM.Using the 829G for resistance measurement is at the moment a little more onerous, as the internal AD 146J fet opamp needs a power supply retrofitted, and the input to the missing panel meter needs to be measured by a DMM, and accuracy will be dependent on the internal precision resistors.Interestingly, the manually set output level (voltage or current) is made using the decade range setting, along with a 15 step coarse adjust setting followed by a single DeYoung pot (23A-10k) providing both medium and fine level adjustment using a neat internal double element pot resistor configuration. The pot is based on US380010 (https://patentimages.storage.googleapis.com/d6/aa/06/f448d371fb6686/US3380010.pdf), and Greg Christenson (@Barbouri) describes it in his blog on a HP 3551A restoration (https://www.barbouri.com/2022/05/27/hewlett-packard-3551a-transmission-test-set/). Initial testing made me think naively that the pot had a bad wiper contact - and even knowing how it adjusts it still takes a bit of getting used to!