Guildline 9154D 'Transvolt' DC Voltage standard - Page 1
Forum section: electronics / general

author: manganin
author_rank: Regular Contributor
timestamp: November 14, 2022, 06:31:01 pm
content: As the name suggests, this is a transportable voltage standard based on saturated Weston cells. The four independent sections allow the detection of excessive drift of any individual cell.Designed for maintaining the Volt in high level calibration labs, but small enough to be easily sent to the national lab for comparison. Built to withstand shipping and recover within 2 weeks. Very compact, only 28 x 35 x 19 cm.This must be one of the last units ever made. Purchased in the early 90s and the latest component date code that I found was December 1990.The temperature coefficient of a saturated Weston cell is quite high, comparable to an unheated LTZ1000.Instead of the traditional bang-bang mercury thermostat and a heavy oven mass to filter out the variation, the 9154D relies on more sophisticated electronic temperature control. The precious cells are mounted inside a vacuum insulated flask to further reduce the required wall thickness and weight.The 9154D has a built in deviation bridge for measuring the cell temperature. The reference divider consists of two precision wire wound resistors. The other branch is made of an ultra-stable glass encapsulated thermistor and a third WW resistor in series with a WW potentiometer. The bridge components are mounted inside the oven to eliminate their temperature coefficient, except the potentiometer, which represents only a tiny fraction of the resistance anyway.The potentiometer scale indicates the deviation from the nominal temperature, when an external voltmeter (connected to the front panel binding posts) detects the null. The scale maximum is only +/-0.02 C which gives an idea of the oven stability.Testing the cells turned out to be a little bit challenging, because the internal lead acid batteries were removed at the time of putting into storage. I remember being told that the instrument should not be operated without the batteries installed.The measurement was carried out last summer in steady 25 C room temperature, close enough to the original 30 C oven. The temperature stability was not an issue, thanks to the high thermal resistance of the vacuum flask and the cells producing no heat.HP 34401A multimeter, 10 Gohm input resistance selected. The readings of all four cells were rock solid with the 6.5 digit meter.1: 1,018373 V2: 1,018372 V3: 1,018368 V4: 1,018373 VThe cell voltages were surprisingly close to each other even after 30 years.1: 0 ppm (reference)2: -1 ppm3: -5 ppm4: 0 ppmThe absolute voltages also well matched the expected value at the approximate 25 C temperature.Source: Precision Measurement and Calibration Vol 3 Electricity - Low frequency, NBS 1968The 9154D is known to suffer from detoriating insulation. In the older examples the foam literally disappears as you can see in this photo. Luckily the one that I have was manufactured after Guildline changed the type of the foam material.Source:https://www.aef.se/Matteknik/Matteknikportal/Bildportaler/Bildportal_G-L/Detaljer/Guild_696/Guildline_696.htm

author: manganin
author_rank: Regular Contributor
timestamp: November 14, 2022, 06:31:43 pm
content: High resolution photos of the printed circuit board.

author: edpalmer42
author_rank: Super Contributor
timestamp: November 14, 2022, 10:31:25 pm
content: Nice looking unit! Congrats!The deteriorating foam wouldn't affect the readings. It's purpose is to stabilize and protect the Dewar flask from physical shocks. But it seems that every type of foam will eventually start to break down and turn to stone, dust or goo - whichever will cause the biggest problems!

author: Vgkid
author_rank: Super Contributor
timestamp: November 15, 2022, 08:01:31 am
content: Thanks for the teardown , I have always liked Guildline instruments.

author: manganin
author_rank: Regular Contributor
timestamp: November 16, 2022, 02:42:11 pm
content: Quote from: edpalmer42 on November 14, 2022, 10:31:25 pmThe reduced insulation certainly affects the control loop balance. Not sure if enough to create problems.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 16, 2022, 04:50:01 pm
content: The heat losses / insulation has usually only little effect on the control loop. It is mainly more effect from the outside / more disturbance the regulator has to work against.For the control loop the relevant points are the heat capacity of the inside and the thermal link from the heater to the sensor.Anyway the main insulation seems to be the vaccum part. The faom may be more mechanical protection than insulation.

author: edpalmer42
author_rank: Super Contributor
timestamp: November 16, 2022, 06:29:11 pm
content: Quote from: manganin on November 16, 2022, 02:42:11 pmYes and no. The insulation is surrounding a Dewar flask. The amount of heat escaping through the Dewar is negligible. The only thing you have to consider is heat escaping through the open end of the Dewar. If the foam there has been compromised it could affect the readings.The same situation arises with precision quartz oscillators. Some are inside Dewar flasks. I've had to deal with a couple that ended up with broken Dewars due to bad packing & shipping. Interesting, but not fun since you end up with a 'Frankenquartz' oscillator instead of an Oscilloquartz oscillator!Ed

author: manganin
author_rank: Regular Contributor
timestamp: November 18, 2022, 01:43:54 pm
content: I wasn't involved, but remember an attempt to modify a 9154D (or C?) for standard resistors, but it wasn't that easy. You don't need to change much to ruin the very fine balance.Must have required a lot of work to make the 9154D stable down to 0.01 C and responding to the outside disturbancies that well. The very small oven mass makes it even more dependent of the control loop design.