Metrology: Methodologies, Uncertainties, and Calibration Certificates - Page 1
Forum section: electronics / general

author: alex-kv
author_rank: Contributor
timestamp: November 07, 2024, 02:49:27 pm
content: Hello everyoneI’m about to enter the field of metrology and its associated calculations and methods. I’ve been personally interested in it for some time, and now an opportunity to apply it to my work has arisen. I’m excited to seize it.currently, I perform calibrations both on-site and at customers' premises. These calibrations are carried out using a K2000 multimeter and shunts that are calibrated by an external laboratory. Additionally, we use current clamps, which are also calibrated externally. A PT100 simulator is calibrated in-house each time the K2000 is freshly calibrated.I've just purchased a DMM7510 and would like to perform all calibrations in-house, knowing that it comes with a DAkkS calibration certificate.Here is the equipment I need to calibrate, for which I'll be preparing a calibration certificate:- K2000 for on-site calibrations (DC voltage only)- 100 mV full-scale shunts: 100A, 300A, and 2000A (resistances ranging from 1 milli-ohm to 50 micro-ohms)- Current clamps (50A to 500A) with a full-scale output of +/- 2V- PT100 simulatorAvailable Equipment:- DMM7510 (with DAkkS calibration certificate)- K2000- Several PSUs (up to 15A)- Fluke 5440B- 34420A (with error 744 “Cal checksum failed, RES corrections” — requires fixing)- K2400 SMU- Shunts (100 mV full scale, for 100A, 300A, 2000A)- Homemade 50-turn Clamp Test BenchI propose to tackle the various subjects in stages, beginning with the calibration of the K2000, as it seems to be the simplest operation.The methodology would involve measuring the Fluke 5440B using both the DMM7510 and the K2000 connected in parallel. This will require stacking two banana plugs on each terminal of the 5440B.DMM7510 settings:Acal if out of 30 daysInput impedance AUTOLine Sync ONAuto Zero ON5PLCShould I have to redo the zero when the measurement range changes?K2000 settings:10PLC (slow mode)Repeat filter ON?For all hot devices:1. Zero the DMM7510 and K2000 using a low-thermal short.2. Connect the leads to the Fluke 5440B and allow the temperatures to equalize.3. Take measurements.The customer instruments I need to calibrate have an accuracy of 0.1%, so it seems reasonable to aim for a maximum uncertainty of 500 ppm. I would appreciate any feedback on this arbitrarily chosen 500 ppm target. The advantage of having a relatively loose uncertainty is that it allows me to take full advantage of the DMM7510’s two years specifications, reducing both the cost of calibrating the 7510 and increasing its availability.Now comes the part I'm less comfortable with: calculating uncertainties.For example, let's take a reading at +10V. The DMM7510 measures 10.000068V with an uncertainty of 2 ppm (from the cal lab's calibrator?) and 23.2 ppm from the DMM. The resulting uncertainty would therefore be SQRT(2²+23.2²) = 23.29ppm. Is this correct?So, I know that the voltage is 10V ± 23.29 ppm when the DMM7510 displays 10.000068V.At the same time, the K2000 displays 10.00026V, with an uncertainty of ±35 ppm at 1 year, according to Keithley’s specifications.That’s fine, but shouldn’t I include the DMM7510’s ±23.29 ppm in the K2000’s calibration certificate when I write it up?

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 07, 2024, 03:05:53 pm
content: HelloCalibrate high current shunt need dedicated equipment , I doubt a DMM7510 can do the job , another problem with BIG shunt is the connection to the circuitRegardsOS

author: alex-kv
author_rank: Contributor
timestamp: November 07, 2024, 05:06:44 pm
content: Right. The DMM7510 was not intended for measuring large shunts, although a measurement of a 100A shunt with the 7510 with offset compensation and 30-minute averaging gave a measurement of 1.0016 miliohms, whereas its external laboratory calibration gave 1.002 miliohms.To measure the shunts, I imagined calibrating the K2400 to 1A using the 7510, then using the same K2400 to deliver 1A to the shunt, and then measuring the voltage across the shunt with the 7510. But then I'd get into a series of manimulations followed by uncertainty calculations that I don't know how to do.I thought I'd start with a simpler calibration procedure, by first calibrating the DC voltage.Regards,Alex

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 07, 2024, 06:37:54 pm
content: HelloI link a useful document on shunt calibrationshunt temperature and connections are mandatory .RegardsOS

author: CalibrationGuy
author_rank: Unknown
timestamp: November 08, 2024, 01:49:36 am
content: I've been in the calibration field for decades. Uncertainty calculations can get very complex. There is a website that can help you and it has many free resources available. Here is the link:https://www.isobudgets.com/I do not have any financial interest or affiliation with the site. Rick Hogan is a nice guy and very helpful. It should help you a lot.Good luck!TomG.

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 08, 2024, 07:45:24 am
content: Quote from: CalibrationGuy on November 08, 2024, 01:49:36 amHelloI agree with the complex side of calculation but before to try to calculate uncertainty , the mandatory step is a use a valid procedure / setup ( ISO 17025) without that it s like built a house of cards on moving sandSOa BOM for all the equipmenta schematica procedurean instruction docRegardsOS

author: Poroit
author_rank: Frequent Contributor
timestamp: November 08, 2024, 09:09:21 am
content: G'day alex-kv,I managed a NATA Lab (Australia) Pressure, Temperature & Electrical for over 40 years and always put my techs through a paid Uncertainty Course.Techs needs good Maths and experience with spreadsheets for calculating Uncertainty budgets.I would suggest you look for the similar equivalent to NATA in France and enquire about Uncertainty Courses.Are you aiming for ISO17025?BTWTrescal have been buying Calibration labs in Oz over the past few years.

author: alex-kv
author_rank: Contributor
timestamp: November 08, 2024, 09:17:13 am
content: Quote from: Overspeed on November 07, 2024, 06:37:54 pmThank you Overspeed.This document on shunt calibration is very interesting, as it takes many factors into account. I’ve had the opportunity to observe a fairly significant temperature drift in various shunts (in the budget model) in devices I’ve calibrated in the lab. In the most recent calibration, involving a 100A shunt, I noted a variation of 80A when the device was cold, which stabilized at 80.05A an increase of over 600 ppm.It seems to me that I’ve read on this forum that, for very high currents, the magnetic field generated by the current can influence the flow of current through the shunt, which may ultimately modify its resistance."The temperature dependence of shunt resistance is quite problematic because, if the shunt is not operated at (relatively) constant current, current calculation can become complicated, as self-heating must be taken into account. This introduces an additional factor: measuring the temperature of the shunt. Where should the measurement be taken? At multiple points? And, of course, you also need a good temperature characterization of the shunt. I imagine a whole new thread would need to be dedicated to this topic (which is, by the way, very interesting).Fortunately, I don’t need to deal with such a level of uncertainty in the calibrations I require at the moment

author: alex-kv
author_rank: Contributor
timestamp: November 08, 2024, 09:24:21 am
content: Quote from: CalibrationGuy on November 08, 2024, 01:49:36 amVery valuable document this "7 Steps to Calculate Measurement Uncertainty". It seems to me that this is an excellent document for getting started in this field

author: alex-kv
author_rank: Contributor
timestamp: November 08, 2024, 10:15:02 am
content: Quote from: Poroit on November 08, 2024, 09:09:21 amHi Poroit,I've presented the subject in a fairly general way so that this thread can be useful to as many readers as possible.I work for a small company that manufactures battery benches. The calibrations I perform, whether in-house or at the customer's premises, are only for the devices we have manufactured. As a result, I provide the customer with a calibration report that is valid for 1 year. There is no mention of uncertainty in the instrument specifications or in the calibration report, only tolerances. I know this may not sound very 'metrological,' but frankly, it would be overkill for the application in question.But yes, I do have some personal 'volt-nuttery' tendencies (I should point out that all the equipment mentioned in my first post, except for the K2000 and the shunts, is mine).Currently, I calibrate benches using the K2000 and shunts that are calibrated by an external lab. As a result, I have calibration certificates with uncertainties for both the K2000 and the shunts, which are renewed annually. My goal is to produce these certificates in-house and send them to the customer along with the bench certificates.Basically, I'm combining one of my passions with my work. So, I need a minimum level of knowledge to calibrate the K2000 and the shunts myself. And while I'm at it, I'd like to go further and learn even more, if possible.Is my approach appropriate?From the company's cost point of view, external training seems hard to justify at the moment.

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 08, 2024, 02:54:14 pm
content: Quote from: alex-kv on November 08, 2024, 10:15:02 amHelloAs you write :I work for a small company that manufactures battery benches. The calibrations I perform, whether in-house or at the customer's premises, are only for the devices we have manufactured. As a result, I provide the customer with a calibration report that is valid for 1 year.And IF you are under the management of a Quality system as ISO9001 that mandatory to respect the ''paper work '' which will linked with your Quality system in case on customer claimsAfter that a question of equipment so YES or NO you have the right equipment to be able to do the right job .That important as ( without to be pessimistic ) if one of the customer of your customer have a fire or any major problem , they will run an audit to check if all the the calibrations have been done following the right way and is/was compliant your ISO 9001 requirements .Some time a perfect job can be assessed as wrong due to paper work problem .For shunt calibration the main concern is the linearization something comparable to a thermocouple so normally full range of the sensor , so 300 Amp current which request high power PSU , try to just measure the shunt resistance value is a bit limited .You can also use a reference shunt and make comparison with your shunt to calibrate , perhaps a welding generator can work as they are quite cheapRegardsOS

author: alex-kv
author_rank: Contributor
timestamp: November 08, 2024, 06:28:43 pm
content: Hi Overspeed,no ISO9001 here.In relation to the measurements and calibrations I need to conduct, accounting for the temperature behavior of the shunt is unnecessary. Current measurement is used to calculate the ampere-hours restored by a battery. When you examine the capacity curve of a lead-acid battery as a function of temperature, it’s clear that the battery—where the ampere-hours are stored—is highly sensitive to environmental conditions. I measured around 6185 ppm/°C on the attached curve at the nominal point. At customer sites, battery temperature is monitored for safety reasons only. My predecessor has already addressed the accuracy of current measurement and regulation on the bench, with comfortable margins. While we could increase precision, that level of accuracy is beyond what customers actually require.That said, characterizing a shunt is something that really interests me. I add it to my to-do list. I think this topic would need a dedicated thread.Quote from: Overspeed on November 08, 2024, 02:54:14 pmWhat you say makes me think that I haven't explained well enough the context in which the calibrated shun is used. When I calibrate a bench, there are 2 shunts in the circuit: the one inside the bench, which I never touch and which is never removed from the bench, and the reference shunt used to measure the current actually delivered by the bench and compare it with the setpoint current.

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 09, 2024, 08:12:00 am
content: HelloOK no ISO9001 but built a robust documentation system regarding testing procedure and report is a mandatory need.A shunt is sensible to temperature , both ambient temperature and shunt temperature shall be recorded , perhaps a Hall sensor as a LEM will be more stable and easier to use.Cable temperature shall be also controlled as copper cable have a poor Tempco and shunt have a low resistance value as I suppose you don't use pulsed current.Shunt are also sensible to connection stability so for calibration purpose that request special care as torque wrench , perfect surfaces ...I link a useful doc see page 5 for temp setupRegardsOS

author: CalibrationGuy
author_rank: Unknown
timestamp: November 09, 2024, 11:57:24 pm
content: I agree with Overspeed. It is truly imperative to have explicit and well documented procedures. It is so very easy to get different results if your testing differs even slightly. When we get our equipment back from calibration, usually from Keysight's Primary Stanards Lab, we do a set of measurements to test not only our equipment but our procedures as well. Don't assume, measure, measure, and measure again. Good luck.TomG.

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 10, 2024, 08:28:15 am
content: HelloA interesting / useful book I link tittle as that a copyrighted book.Iso.10012.2003 can be also a good readingHere after some information from another sourceThe good manufacturing practice (GMP) Calibration requirements and objective evidence includethe following:• Routine calibration frequency: the objective evidence is a calibration schedule• Accurate and concise documentation for purposes of objective evidence:A clear second-level procedureWork-instruction-level documents for calibrating each piece of equipmentA signed and dated calibration record with all of the appropriate informationThe record shall include the following, as necessary:- the description and unique identification of the equipment manufacturer, type, serial number, etc.;- the date on which the metrological confirmation was completed;- the result of the metrological confirmation;- the assigned interval for metrological confirmation; identification of the metrological confirmation procedure- the designated maximum permissible error(s)- the relevant environmental conditions and a statement about any corrections necessary- the uncertainties involved in calibrating the equipment- the details of any maintenance, such as adjustment, repairs or modifications carried out; any limitations of use;- the identification of the person(s) performing the metrological confirmation;- the identification of the person(s) responsible for the correctness of the recorded information- the unique identification (such as serial numbers) of any calibration certificates and reports, and otherrelevant documents;- the evidence of the traceability of the calibration results- the metrological requirements for the intended use- the calibration results obtained after and, where required, before any adjustment, modification or repair.• Use of traceable standards: certificates that contain traceability numbers and limits of uncertainty• Provisions for remedial action (when an instrument is, for example, found to be out of calibration):a strong and inclusive nonconforming corrective action form used as a tool for quality review boarddecision makingI link two documents from Euramet website , which can be used as a ''template''RegardsOS

author: tszaboo
author_rank: Super Contributor
timestamp: November 10, 2024, 12:05:40 pm
content: Quote from: alex-kv on November 08, 2024, 09:17:13 amBest way to calibrate shunts in order is:1. Same way as before2. The way it's used under real world conditionsFirst should be obvious, changing procedure in theory makes previous certificates invalid, since you are comparing apples to oranges. The second one is tricky. I used to make this calibrator at work, where 4 current ranges were calibrated with 4 large hundred watt shunts. The shunts were used to translate the current into voltage, to be measured by DMMs. Their thermal load was 1-10th of their rating and their duty cycle in the calibrator was quite small. In this case the best is to have the shunts calibrated without constant load, and without any heat-up.

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 10, 2024, 03:17:19 pm
content: Quote from: tszaboo on November 10, 2024, 12:05:40 pmHelloI agree but in this case it's seems that a comparison between one installed shunt and one other which is use as reference ( valid calibration ) , and in the goal to validate a test bench so I think that not truly a metrology calibration but a results validation / proof .On a test bench that mandatory to check first if the sensor in the range of full use ( one low , one in the medium range and the last over the maximum value used to be able to check the linearization ) and a preliminary check shall be done on the sensor parameters regarding the thermal load level and the connections shape / bolt torque in the case of a shunt , as a shunt is a bit tricky to use , more than a Hall sensor even in a Hall sensor is not so simple to use .The right way way is still :write what I plan to do before in detail , do step by step what I have written after and analyse the results to be able to make validations .That could be interesting to know what is load in Amp use on the shunt as '' shunt value '' is a maximum and that not recommended to load a shunt at the maximum current under constant load , same for the wires .RegardsOS

author: mendip_discovery
author_rank: Super Contributor
timestamp: November 10, 2024, 07:50:26 pm
content: Calibration of Shunts has always been contentious. I do them via my 17025 accreditation, but my auditor has often given a raised eyebrow the ones I do, have been either for the lab's use or within the range of the current I can supply. My method is 5 mins on, 5 off etc for 5 measurements. Swap connections around to remove the EMF side of things and repeat. Take an average of those readings and then from that give a resistance measurement. However, if I were to take on more of this kind of work I would get a bigger power supply, one that can generate significant AMPs.I would recommend some of the UKAS (UK's 17025 Accreditation people), Joint Committee for Guides in Metrology (JCGM), ILACLAB48 - Decision Rules and Statements of ConformityM3003 - The Expression of Uncertainty and Confidence in MeasurementVIM - International Vocabulary of MetrologyGUM - Guide to the Expression of Uncertainty in MeasurementFor the budget, you need to think about,Imported Uncertainty (from your cal cert) of k=2 so it can be divided by 2 as a Normal DistributionResolution, you can divide the resolution of a device by 2 as the 1/2 digit can be rounded up or rounded down, then it can be divided by sqroot(3) as a rectangular distribution.Specifications (Relative), often shown as % or a µV/V etc. for extra buffer use rectangular aks sqroot(3) but depending on the manual and the actual stability of the meter it can be classed as Normal so a divide by 2 is possibleSpecifications (Absolutute), same as above but it is the bit shown as a fixed value.Repeatability, you need to do some tests with a unit that you might measure and repeat the tests several times. I would break down my setups and start again which is technically reproducibility but again I wanted to give myself room. This would be a normal distribution (68%) but one where you end up using a divisor of 1Thermal EMF, take the lab conditions and depending on the leads you have and the connectors etc add some 0.3µv/V per °C depending on the metals involved.Root Sum Sq that all and you get a rough approx of the Uncertainty. There was a push for a while for lab scopes to be a fixed value but thankfully they are going back to µV/V + µV type setup. Round your numbers to the nearest 2 digits. 1.253 µV is 1.3 µV, 0.2136 µV is 0.21 µV.I suggest having a play withSuncalas that is Python based and a good way to get your head into it.Attached is a basic Uncertainty calculator I did for a 3458A in the 120 mV range.

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 11, 2024, 10:52:02 am
content: HelloRepeatability is a crucial parameter as without a ''bomb proof '' repeatability that just gambling regarding the results .The ASTM E691 is a very useful documentRegardsOS

author: alex-kv
author_rank: Contributor
timestamp: November 15, 2024, 02:01:53 pm
content: Out of curiosity, I conducted some EMF tests on a 300A shunt I had laying around.The test setup consists of a DMM measuring the voltage across the shunt, with no current applied. A dual-type K thermocouple thermometer is used to measure the temperature at the shunt's sense connection.Note: I had to ensure that neither of the thermocouples was electrically shorted through the shunt, to avoid interfering with the thermometer's readings.Only one side of the shunt is heated with a hot air gun.1. Shunt as found. Oxidization around the sense terminals. Dark brown brass washers.A 33 °C increase produced 56.6 µv. The shunt's full scale is 100 mV. So around 17.2 ppm/°C drift.2. Sand paper on the shunt sense area. New brass washers. Sand paper on the crimp terminals, so copper-brass junction here.A 37.3 °C increase produced 63.9 µV. Around 17.1 ppm/°C. I expected a bigger shift here.3. I removed the crimp terminals to test with copper directly on the shunt sense zone.A 40.2 °C increase produced 71.4 µV. Around 17.8 ppm/°C.Only one side of the shunt is externally heated, so the power joints of the 'reference part' and the large brass part are not at the same temperature. This could introduce another source of thermal EMF.EDIT: resize images

author: alex-kv
author_rank: Contributor
timestamp: November 15, 2024, 02:22:57 pm
content: After over a week of research into this new field —uncertainties and other mathematical operations associated with metrology— I estimate that it will require more work than I initially expected.Quote from: Poroit on November 08, 2024, 09:09:21 amQuote from: Overspeed on November 09, 2024, 08:12:00 amQuote from: CalibrationGuy on November 09, 2024, 11:57:24 pmThis wasn't my initial objective, but as I read through the various documents provided in the different posts, I realize that ISO 17025 should ultimately serve as a model for my approach.Quote from: Overspeed on November 09, 2024, 08:12:00 amI imagine that these precautions must be taken to achieve as even a contact resistance as possible on both sides of the shunt, which would result in similar heating. Is this correct?Quote from: Overspeed on November 08, 2024, 02:54:14 pmThis gives me ideas for a shunt test bench. 160A should be easy to obtain, but not 2000A. And it's also necessary to have a reference shunt, which is another problem.In any case, calibrating a 1A current source with the DMM7510 will not be enough.

author: alex-kv
author_rank: Contributor
timestamp: November 15, 2024, 02:42:37 pm
content: Quote from: Overspeed on November 10, 2024, 03:17:19 pmIt seems to me that verification is based on calibration, followed by a comparison of the calibration results with the device's specifications.JCGM 200:2012 page 31 2.44: "verification - provision of objective evidence that a given item fulfils specified requirements."How to get "objective evidence" without performing a calibration? Do I confuse apples and oranges?

author: alex-kv
author_rank: Contributor
timestamp: November 15, 2024, 02:58:38 pm
content: Quote from: Overspeed on November 10, 2024, 03:17:19 pmCan you please elaborate on the Hall sensor? I have used a closed-loop Hall effect sensor before, and I remember it was sensitive to Earth's magnetic field. So, once the sensor is in place and ready to use, it should not be moved. Temperature drift should be accounted for, and I have never seen any hysteresis characterization in the datasheets

author: mzzj
author_rank: Super Contributor
timestamp: November 15, 2024, 06:59:33 pm
content: Quote from: alex-kv on November 15, 2024, 02:58:38 pmGet a LEM/danisense/danfysik Ultrastab fluxgate sensor and call it a day. You still need to measure the secondary current but 100mA is lot easier to measure with decent DMM than 150A.1ppm linearity, 0.05ppm resolution and 0.3ppm/c tempco are hard to beat.

author: mzzj
author_rank: Super Contributor
timestamp: November 15, 2024, 07:11:39 pm
content: Quote from: mendip_discovery on November 10, 2024, 07:50:26 pmI'd just note the thermal EMF offset voltage without test current before and right after running the test current.Typically it seems offset voltage is rather minor problem with most shunts. I*R heating and associated resistance tempco are much bigger problem most of the time.Homebrew 1 micro-ohm copper shunt was rather extreme example of this: EMF stable to within 30nV but 3900ppm/cel temperature coefficent on resistance.

author: Kleinstein
author_rank: Super Contributor
timestamp: November 15, 2024, 11:02:00 pm
content: How much thermal EMF develops at a shunt depends on the symmetry. Ideally the temperature would be the same on both sides and thus no error from thermal EMF. It does not take that much to create some asymmetry, e.g. from different heat losses at the cables or a not ideal electrical contact for the current path that heats up. Good shunt should use low thermal EMF materials, but not all do.

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 16, 2024, 09:50:55 am
content: Quote from: Kleinstein on November 15, 2024, 11:02:00 pmHelloI agree but I will add this pointThe power in the shunt is a critical parameter , make 50 Amp continuous with a 300 Amp Shunt is not the same as make 280 Amp with a 300 Amp shunt and this point is also linked to the fact to run comparison measurement with the same type of shunt .A critical point on shunt measurement is the connection , surface shall be clean with a good shape contact shape and also a similar / same screw torque as contact pressure is a important parameter .Industrial shunt are not always to not often '' high quality material '' as Manganin but more often in cheaper copper nickel alloys so be aware of wild tempco .These problem can be partially solved by a robust procedure ( torque , contact checks ..) and a temperature / resistance value table .RegardsOS

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 16, 2024, 10:34:29 am
content: HelloTo avoid make massive quote , I have copied the paragraphRegarding procedure : As your goal is to run calibration and generate valid results , a written procedure with pictures / drawings is mandatory to be able to duplicate always the same things to avoid any delta in the results.Writing a procedure is not a punishment as that an usual engineering document , no need to write an encyclopaedia too but something as a tool able to be improved ..Regarding repeatability , before to claim that a result is GOOD , this results shall be demonstrated by a repeatability test , in various industries , test as Anova R&R are very common .Whatever you are or not under Quality management system , these rules are valid and useful .RegardsOS

author: alex-kv
author_rank: Contributor
timestamp: November 17, 2024, 08:16:38 pm
content: Hello,I've tried to produce a calibration procedure. It is available as an attachment.So far, I have only processed the 100 mV range. I still need to figure out how to integrate the measurements into the mendip_discovery Excel file.Alex

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 18, 2024, 08:32:50 am
content: Hello2 interesting documentsone Korean calibration methodone Fluke '' how to measure power coefficient '' this document include clear schematicsI will post longer todayRegardsOS

author: alex-kv
author_rank: Contributor
timestamp: November 19, 2024, 10:07:46 am
content: HelloThank you Overspeed. It seems you have a well-stocked library of very interesting documentsI updated the procedureAlex

author: alex-kv
author_rank: Contributor
timestamp: November 19, 2024, 01:23:43 pm
content: When applying the procedure, I wonder if the quality of the calibration could be improved by using the statistical functions of the devices and taking an average of 50 measurements. The average will span500 PLCs2500 PLCs for each DMM. Since it's not possible to obtain a stable value exactly as indicated by the calibration certificate of the 'standard' DMM, I calculate the gain coefficients of the positive and negative values from the standard readings and then apply them to the UUT readings.I updated the procedure accordingly.EDIT: corrected number of PLCs

author: alex-kv
author_rank: Contributor
timestamp: November 19, 2024, 01:38:55 pm
content: Here is a practical example of the calculation steps in the procedure, given that the calibrated values of the standard DMM for 100 mV and -100 mV are 100.0012 and -100.0008 respectively.DMM7510 AVG 50RDGS 100mV = 100.00161 mVDMM7510 AVG 50RDGS -100mV = -100.00128 mVK2000 AVG 50RDGS 100mV = 100.0031 mVK2000 AVG 50RDGS -100mV = -100.0031 mVPoscoeff = 100.0012 / 100.00161Negcoeff = -100.0008 / -100.00128[ EDIT:Poscoeff = 0.9999959Negcoeff = 0.9999952]"Measured value" for the UUT's cal cert:100.0031 * 0.9999959 = 100.0027 mV-100.0031 * 0.9999952 = -100,0026 mVHave I done things right?Alex

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 21, 2024, 07:29:03 am
content: HelloWhen you run a calibration your procedure shall match the exact way / method of measurement you will use to compare '' apple with apple '' OR you run the standard calibration procedure as provided by the manufacturer .If you chase ultimate accuracy ( precision ... ) and if you select an average measurement on 50 measurements OK why not , but you shall use the same for your daily measurement.I never use the last digits of a instrument IF I need a real / better value I switch to a 7.5 or a 8.5 digits instrument . With low to very low voltage as shunt output voltage that also a solution to use a low noise preamp .RegardsOS

author: Kleinstein
author_rank: Super Contributor
timestamp: November 21, 2024, 09:02:19 am
content: One should also include a zero measurement - not abosultely necessary to check the gain, but it would help to detect problems with linearity. Once set up the extra reading does not take that much time.

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 21, 2024, 12:05:20 pm
content: Helloa doc on shunt tempco vs resistance changeRegarding the calibration I agree with Kleinstein on linearity , best is to try a 3 point calibration 0 V mid range so 5 V and full range 10 V if that a 10 V rangeThat also possible to limit reduce the calibration range to be closer to the measurement need as for example if you plan to measure between 0 and 5 V that better to run 0 V 2.5 V and 5 V calibration rather than the full range as 10 VRegardsOS

author: cscaccetti
author_rank: Newbie
timestamp: November 21, 2024, 08:25:05 pm
content: Did a scope expansion for DC energy measure. So not only dealing with just DCI measure, but DCV, time, simultaneity of measure, and more. You are going to have so much fun.Get a danisense DCCT, can't beat it. Like 10 ppm, in series with your shunt, and compare. The danisense guys, were some of the best from LEM. I've tested both the ultrastabs and the DS series, both are incredibly good, the danisense edges out the LEM IMO. But likely, given the level of your equipment, it wont matter, so get what ever is cheaper. They also have great acd/dc properties, so could open up your lab to ac measure later as well.As for the thermals of the shunt, you either go one of two ways:You energize to current level, hold, and stabilize temp. What I have found with this is that, shunts can take a significant amount of time to stabilize to a level of very low variability. Like over 30 minutes. Then doing that for a number of test points, make this method incredibly time consuming.Or either swap connections, or shut on off, and negate thermal EMFs. I do something like 5 second measure off, 5 second measure on. 5 second measure off. Average before and after and subtract from measure. 5 repeats. Point being quick measures to mitigate self-heating. high dTemp/dTime kills ability to temp correct, and will throw erroneous results.Also looking at your pictures, need better metal matching. The owner of Ohm-labs, Jay has great material, and is a good source of knowledge when it comes to all things resistance and testing. Sadly he is mostly retired, so he may not be as available to chat as he used to.For the thermal characterization, you need a more homogenized environment, like an air bath. But you can go more junkyard approach, with a box and a fan and temp sensor. If you are curious to see what type of equipment it takes to do this work, what I typically do is research who the players are in the test equipment field, then I look for the ISO17025 scope, and then find the measure, and measure range to find the calibrating equipment.There is so much more, but my brain's quite scrambly from not sleeping. Relatively new father (1y.o.), much harder than uncertainty budgets.

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 25, 2024, 07:53:12 pm
content: HelloAn interesting 100 Amp current circuitRegardsOS

author: Hydron
author_rank: Super Contributor
timestamp: November 25, 2024, 10:06:10 pm
content: Quote from: Overspeed on November 25, 2024, 07:53:12 pmInteresting that they are running the IGBT in it's linear region (I was under the impression this was a good way to make the smoke come out) - I guess they are being conservative enough (or just lucky) to get away with it?

author: Overspeed
author_rank: Frequent Contributor
timestamp: November 27, 2024, 09:38:01 am
content: HelloYes I agree thermal effect is real concern for this circuit but nothing say they stay ''ON'' a long time and they can also have thermal controlQuestion how are managed the static relay ?RegardsOS