Mini teardown: Hartmann & Braun vintage precision shunt 150A 60mV 0,05% - Page 1
Forum section: electronics / general

author: carl_lab
author_rank: Frequent Contributor
timestamp: September 08, 2017, 11:15:40 am
content: Found it in a dumpster:"H&B 150A Präzisions-Nebenwiderstand" (precision shunt)Does anybody have more info about this item (resistance material/alloy etc.)?I can't say if the golden color comes from resistance alloy or just from the lacquer coating...Can it be used for metrological purpose?Which meaning has the "2 on a star" mark?Which meaning has the "0.005A" labeling?

author: HighVoltage
author_rank: Super Contributor
timestamp: September 08, 2017, 11:50:04 am
content: I have a very similar looking one with 25 Ohm and similar writings on it.But I have no explanations.You got lucky to have such a dumpster.

author: carl_lab
author_rank: Frequent Contributor
timestamp: September 08, 2017, 12:16:55 pm
content: Do you have an idea about varification of accuracy of that item?I have access to high current power supplies up to 50 or 60A, but I don't know if constant current output mode of these standard PS will be stable enough to use them for calibration purpose.What's the usual method to calibrate high current shunts in the sub-milliohm range?

author: AG7CK
author_rank: Regular Contributor
timestamp: September 08, 2017, 12:33:06 pm
content: Nice box. I have seen class 0.1 0.2 0.5 and 1 before, but never 0.05.The 150A calibrated 3-blade shunt will nominally be 0.060V/150A which is 0.0004 ohm or 0.4 milli-ohm. In order to check if the resistor is +-0.05% you will have to resolve 1/2000th of this - i.e. 0.2 micro-ohm. So you will have to check if the resistor measures between 0.0004+-0.0000002 ohm, i.e. it should measure in the interval [0.0003998, 0.0004002] ohm.Suppose you - just as a crude check - use a several thousand dollar 34420A 7.5 digit micro-ohm meter on lowest range 1 ohm. The 7.5 digits will resolve 0.1 micro-ohm, so it will present a reading of the format 0.0004xxx as is needed.The problem imo is that the meter's best spec is 0.0015+0.0002 which in Agilent terms means that absolute best accuracy (independent of reading value) is 0.0002% which is 2ppm or in the case of 1 ohm range 2 micro-ohm. So in a sense the inaccuracy of the meter is 10 times what you need to detect. Am I correct? If so, how can this shunt adequately be checked?Can't wait for the sub ppm metrology wannabes to chime in here.EDITI do understand that you can find a 150A source and a voltmeter w/ range 100 mv - both suficiently better than 0.05% - and deduce 0.0004 ohm +- 0.05%. But can one measure the resistance on the lab bench with standard precision gear?

author: carl_lab
author_rank: Frequent Contributor
timestamp: September 08, 2017, 01:32:47 pm
content: I don't think you can measure resistance in this range with "normal" lab equipment.The problem I see, is interdependence of resistance and current because of warming and TC of resistance alloy.So checking resistance by very limited currents of a standard micro-ohmmeter probably is nearly useless.I also cannot supply much more than 50-60A by standard power supplies (with unknown stability), so I have to check actual current by another precision shunt in series (I could use a Burster 1282 precision shunt, but it is limited to 20A and 0.02%, iirc)...Any helpful ideas appreciated...

author: manganin
author_rank: Regular Contributor
timestamp: September 08, 2017, 01:47:12 pm
content: Quote from: carl_lab on September 08, 2017, 11:15:40 amThat is a manganin meter shunt, designed to work with some specific (H&B) moving coil instrument. Don't expect it to be accurate when connected to a modern high input resistance digital multimeter.Quote from: carl_lab on September 08, 2017, 11:15:40 amNot metrology grade, but there are a few easy to do improvements:1. Enlarge the binding post mounting holes, so that the resistive element is free to expand when warming up.2. Prepare flexible fixed cabling which you never disconnect at the shunt end. Change in the thumb screw torque can introduce a change up to several hundred ppm.3. Put it in mineral oil. That will help with the small size / heat dissipation area, but also gives you much better control over the probably not so optimal TC.Quote from: carl_lab on September 08, 2017, 11:15:40 amInsulation test voltage class.Quote from: carl_lab on September 08, 2017, 11:15:40 amThe moving coil instrument full range.

author: AG7CK
author_rank: Regular Contributor
timestamp: September 08, 2017, 01:59:39 pm
content: In this link is a picture of a H&B (moving coil) watt meter with a similar star and a lot of other symbols. Would be nice to know what they all mean (DC/AC etc. are obvious, but some I have never seen before).https://www.alte-messgeraete.de/elektrotechnik/hartmann-braun-frankfurt-a-m/labor-wattmeter/

author: carl_lab
author_rank: Frequent Contributor
timestamp: September 08, 2017, 02:02:36 pm
content: Thanks for your reply, Manganin.Quote from: manganin on September 08, 2017, 01:47:12 pmThat's what I guessed.To use the shunt with high input resistance instruments (>>1MOhm) I have to parallel a 12 ohm load (= 60mV/5mA)?

author: carl_lab
author_rank: Frequent Contributor
timestamp: September 08, 2017, 02:14:34 pm
content: Quote from: manganin on September 08, 2017, 01:47:12 pmIf I enlarge the holes to allow free expansion of the shunt element, the binding posts could not absorb mounting torque from the thumb screws anymore - is that the reason for need of flexible cabling?Why thumb screw torque affect shunt resistance in such a high magnitude?

author: Vtile
author_rank: Super Contributor
timestamp: September 08, 2017, 02:29:08 pm
content: Quote from: AG7CK on September 08, 2017, 01:59:39 pmVDE 0410 / ISO xxxxxxx specifies these markings.

author: carl_lab
author_rank: Frequent Contributor
timestamp: September 08, 2017, 02:38:48 pm
content: Quote from: manganin on September 08, 2017, 01:47:12 pmWhat TC would you expect?

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 08, 2017, 04:42:10 pm
content: Nice find!The number in the star says the test voltage in kV (here 2kV). A star without a number is 500V. A star with a 0 means not tested. I had to dig out my old Elektronik Tabellen book from 1991 to freshen up my brain.

author: Twoflower
author_rank: Frequent Contributor
timestamp: September 08, 2017, 04:54:29 pm
content: Quote from: AG7CK on September 08, 2017, 01:59:39 pmI's hard to see, but the 0.2 seems to be the accuracy, the underlined part of the frequency range is the base operation area, followed by the orientation for the operation (horizontal), then test-voltage and the last one, the box, is unknown to me.

author: AG7CK
author_rank: Regular Contributor
timestamp: September 08, 2017, 10:18:07 pm
content: In principle, yes. If the meter is supposed to draw 5 mA f.s. then it should have 12 ohm coil impedance. But the error introduced by not shunting the 0.0004 ohm with 12 ohm is 0.0033%. So it is somewhat a question of mathematics pedantry.Thanks to Vtile and Twoflower for the symbols explanation - I guess the box on the watt meter is a shielding sign.

author: carl_lab
author_rank: Frequent Contributor
timestamp: September 09, 2017, 04:32:27 pm
content: I had a look into the manual of our Burster 1282 precision shunt, that is rated 0.02%, TC< 10ppm/K.It is also made of manganin, so manganin seem to be not the worst choice.https://www.burster.de/fileadmin/user_upload/redaktion/Documents/Products/Manuals/Section_1/BA_1282_EN.pdf

author: free_electron
author_rank: Super Contributor
timestamp: September 09, 2017, 04:41:21 pm
content: German has such descriptive words.. Nebenwiderstand.A 'resistor' (widerstand) you put 'next' (neben) to an existing one to carry the current.Compare that to english. shunt. what the hell does that describe ? nothing ...actually the word 'widerstand' means 'something that stands against' the current.

author: TiN
author_rank: Super Contributor
timestamp: September 09, 2017, 06:59:25 pm
content: free_electronWe missed you in metrology section.

author: carl_lab
author_rank: Frequent Contributor
timestamp: September 09, 2017, 08:14:04 pm
content: Quote from: free_electron on September 09, 2017, 04:41:21 pmI never use/used the very retro-ish word "Nebenwiderstand" in german.I always use the word "shunt", because it's much shorter and everybody know it's function anyway.Also I think "Nebenwiderstand" associates something like "Nebenschluss" or "Nebenschlussmaschine" that has to to do with bypassing or wiring two items in parallel, instead of wiring in series what is correct for using a shunt.

author: HighVoltage
author_rank: Super Contributor
timestamp: September 10, 2017, 12:16:05 pm
content: Actually I never used or heard the word "Nebenwiderstand" outside of textbooks.Everyone in Germany also used the word shunt in engineering.Another word being used is: "Kalibrierwiderstand" = Calibration Resistor.

author: e61_phil
author_rank: Frequent Contributor
timestamp: September 10, 2017, 09:21:14 pm
content: I worked at the university and in all student labs the term "Nebenwiderstand" was used instead of "shunt". However, outside the university nobody call it "Nebenwiderstand"

author: HighVoltage
author_rank: Super Contributor
timestamp: September 15, 2017, 11:29:16 am
content: I got my Hartmann & Braun vintage shunt out of the cabinet today and opened it up.Here are some pictures:I have this one since the mid 80s but I have no idea how old it really is.This one came from the University.It looks like the calibration was done by drilling holes of different sizes in to the resistive material.The resistor material is brazed in to the brass studs.

author: carl_lab
author_rank: Frequent Contributor
timestamp: September 16, 2017, 10:55:22 am
content: Thanks for the pictures, HV.It looks like the little younger brother of my H&B shunt.