Logging Voltage

[Voltmanbucks]

Hi I am volunteer at a Charity in High Wycombe called Central Aid. We PAT test white goods inclding electric cookers. The elements would often fail a PAT but need to be thermally conditioned by running for up to 30 minutes to remove moisture from the internal element insulation and reduce leakage current.

To do this we have a current leakage tester , the leakage is given by measuring a voltage across a resistor and converting that to leakage current in mA.

The voltage is shown on multimeter and ranges about 0-500mV. I observe the output for every element recording initial voltage, peak and ultimate stable value. The test can take over an hour for each appliance!

The voltage varies wildly in that range and can show a range of peaks before stabilising,

My question is would a budget multimeter oscilloscope record each test for me, voltage versus time in minutes, graphically in my absence so I can do other tasks?

And if so which make and model please?

Kind regards

Ian

 

[danadak]

Yes, a logging DVM or a DAQ system. An oscilloscope maybe overkill but can do it. If
it has "roll" or "trend" mode, but beware its longest sweep times maybe not enough
for you.

How many do you have to test at a time ? To what accuracy ?

If you go for low cost versions make sure charing software included.

Data Acquisition (DAQ)

Data Acquisition (DAQ) products from DATAQ Instruments for USB, Ethernet, and Wifi. Starter kits from $59.

www.dataq.com

Data Acquisition System (DAQ) Complete Guide [Updated 2024]

Data Acquisition (DAQ) is sampling real-world signals to digital for computer processing. Unlike tape or paper, it's digital and manipulatable by software.

www.logic-fruit.com

Data Acquisition Systems | LabJack DAQ Systems Analog & Digital I/O

Superior Data Acquisition Systems to collect analog & digital sensors. Log, automate and test. Use software like LabVIEW, MatLAB, Python, C, C++, DAQFactory

labjack.com

Data Acquisition

digilent.com

Regards, Dana.

 

[Voltmanbucks]

Dana

Thank you.

I probably have not phrased my question well. I don't want to physically plot or datalog anything. I just want to observe a trend 0-500mv AC for half an hour as it develops on a screen and make some notes.

Cheers

Ian

 

[Voltmanbucks]

I only test one element at a time +/- 2mV would be fine.

 

[Nigel Goodwin]

Hi I am volunteer at a Charity in High Wycombe called Central Aid. We PAT test white goods inclding electric cookers.

Why are you PAT testing cookers anyway?, PAT stands for Portable Appliance Test, and a cooker isn't a portable appliance - and therefore doesn't come under PAT rules. As part of my previous job I PAT tested countless items, but NEVER a cooker, or anything else that doesn't require testing. Interestingly, the PAT tester was one of the few things I took away when the company closed.

If I had ever wanted to leakage test a cooker, I would have used a Megger - we had an old ex-WD hand wound one

The issue with using a multimeter/scope is the long timebase required - I doubt many full size scopes would run that slow?.

As has been mentioned, a 'logger' is what you require - and you could easily make your own using an Arduino, there are countless logger examples out there.

 

[Voltmanbucks]

I am a trained PAT tester so I guess I know what PAT means.

A cooker is a fixed appliance but we have them given as donations in a range of good to poor condition.

We sell them as safe and functional and therefore have duty of care to ensure that is true. Some of them fail and are repaired , some of them are so unsafe they are scrapped, they fail on insulation resistance, earth continuity or leakage current. A few of them would have been potentially lethal.

The elements behave quite randomly during the test but a typical trend sees early peaks folowed by a reduction in leakage and ultimately a low stable plateau.

I don't want to log the data permanently or store in memory , I only want to see the trend develop as the element heats up, dries out and stabilises with respect to leakage current. I then record the key parameters as stated in my original post.

Can you identify the instrument I need please?

You are right I do need a long timebase at twenty minutes

 

[Voltmanbucks]

This article explains the issue with elements that have been stored for extended periods or in damp conditions

Dealing with moisture inside electric heaters | Plant Engineering

Those who work with electronics usually equate water and electricity as a bad combination — and for good reason. Labels can be found on many kitchen | Plant Engineering

www.plantengineering.com

Not every cooker has an issue of course but its quite normal for us to record high leakage initially.

 

[ZipZapOuch]

I am a trained PAT tester so I guess I know what PAT means.

I, somehow, knew exactly why a charity would be testing a stove. I'm sorry it was not obvious to other members.

A small Arduino microcontroller with a very simple program connected to a laptop with a USB cable can be used to do what you need.

The Arduino-based microcontroller can continually measure a voltage (on a 0-1023 scale) and send to the PC. The Arduino IDE (software on your PC) can monitor each measurement and display them as a chart vs time. Most people don't even use the serial monitor in chart mode (or know it exists) but it's really convenient and easy.

The software is free, a genuine Arduino microcontroller costs about $20 or a knock-off is about $3-$5. You'll just need to wire some probes to the Arduino. It can all be powered by your USB port.

 

[danadak]

Dana

Thank you.

I probably have not phrased my question well. I don't want to physically plot or datalog anything. I just want to observe a trend 0-500mv AC for half an hour as it develops on a screen and make some notes.

Cheers

Ian

The DAQs will do that easily for you. Software done, HW done, plug and play.

Regards, Dana.

 

[Voltmanbucks]

Thank you ZapZap and Dana I have a tiny workspace and don't really want to set up a PC. Thanks for you understanding about testing stoves. Is there a stand alone piece of kit up to £200 that would perform this function, something like a budget multimeter oscilloscope please?

Like this

https://www.amazon.co.uk/Oscilloscope-Multimeter-Electrical-Automotive-Electronics/dp/B0CN3B7VP6/ref=asc_df_B0CN3B7VP6/?tag=googshopuk-21&linkCode=df0&hvadid=676282217247&hvpos=&hvnetw=g&hvrand=10029991309508953257&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9046617&hvtargid=pla-2274300806534&psc=1&mcid=248153e71a34319791c5872793b7d255&gad_source=1

But as Nigel said would it support timebase of 20 mins?

 

[Nigel Goodwin]

Thank you ZapZap and Dana I have a tiny workspace and don't really want to set up a PC. Thanks for you understanding about testing stoves. Is there a stand alone piece of kit up to £200 that would perform this function, something like a budget multimeter oscilloscope please?

Like this

https://www.amazon.co.uk/Oscilloscope-Multimeter-Electrical-Automotive-Electronics/dp/B0CN3B7VP6/ref=asc_df_B0CN3B7VP6/?tag=googshopuk-21&linkCode=df0&hvadid=676282217247&hvpos=&hvnetw=g&hvrand=10029991309508953257&hvpone=&hvptwo=&hvqmt=&hvdev=c&hvdvcmdl=&hvlocint=&hvlocphy=9046617&hvtargid=pla-2274300806534&psc=1&mcid=248153e71a34319791c5872793b7d255&gad_source=1

But as Nigel said would it support timebase of 20 mins?

No, the maximum timebase range in the specs. of that device is only 10 secs per division - I've just checked my Rigol scope (seeing as I'm sat next to it) it's maximum range is only 50 seconds per division.

 

[danadak]

https://www.dataq.com/resources/pdfs/datasheets/di-1100-usb-data-acquisition.pdf

More res - https://www.dataq.com/products/di-2108/

Software https://www.dataq.com/resources/pdfs/datasheets/di-2108-usb-daq-datasheet.pdf

https://www.dataq.com/products/di-2108/#software Windaq

This will do as slow as 2.2 samples / hour, and log / display the data into the next century.......or
in your case up to 160,000 samples / sec....or anything in between.

Contact them with your total requirements to make sure you get the best lowest cost choice.


Regards, Dana.

 

[Voltmanbucks]

Nigel , Danadak thanks again, looks the job!

I have also identified the Fluke 289 with logging and trending, it doesn't give you a real time refreshed trend but hit the buttons after 20 mins and it gives you a full historic trend. About £800

 

[danadak]

The true RMS accuray, .4%, 500 mV range, will not give you +/- 2
mV accuracy you wanted.

The £800 will not meet your £200 budget you stipulated.......

 

[Voltmanbucks]

Truth Danadak, I think I overstated the accuracy I need though 0.4% will suffice, and maybe I will chat up the boss for some more cash! Its a very versatile instrument. I will review against the Dataq unit Cheers pal.

 

[ZipZapOuch]

Truth Danadak, I think I overstated the accuracy I need though 0.4% will suffice, and maybe I will chat up the boss for some more cash! Its a very versatile instrument. I will review against the Dataq unit Cheers pal.

Also consider your safety (user safety) of each option. The Fluke will be fully specified and designed for user safety and clearly states max input voltages.

The DatAQ is not so clear on max voltage, isolation from power supply and more.

It would be sad if a safety inspector is injured by his own equipment.

 

[danadak]

Max inputs are stated in the 16 bit solution, but not isolation.

Can be operated stand alone, but no display while logging in progress.

 

[Tony Stewart]

Leakage current is due to contaminants and if moisture is removed to pass the test, it can get wet when cleaned. I would be more concerned about the contaminants and removing them than trying to make it pass by heating it up. Water is an insulator until it is contaminated.

Test equipment can be made very inexpensively to measure 0.1 Ohm ground cable and 230Vrms leakage. I would consider doing a DC HIPOT test with a diode quadrupler and spend more time on figuring out how to reduce the contaminants and 1 minute to do all the testing. If adding water after testing causes a retest to fail, that would confirm my suspicions.

I could design the low cost tester, and a safe test plan.

 

[Voltmanbucks]

The elements are integrated into the hob and stove and don't get "wet" the Magnesium Oxide powder insulator adsorbs moisture from the air, via the end caps, during extended storage in damp conditions such as unheated houses and outhouses. I think the link to the article I attached explains that. when sold the units are indoors , in regular use , and this phenomenon is not an issue. More modern cookers, from new, now have infra red and or induction hobs which eliminate the problem entirely.

Thanks though Tony I am so impressed with all the helpful responses I have had on this forum. I have now purchased a Fluke 289 for this task to compliment our existing PAT test instrument.

 

[Tony Stewart]

I once experienced a major wine spill on a stovetop burner. It had soaked in over night.
I thought I could burn it off, instead it self-destructed acting like a sparkler and slowly burnt off off all the MgO from the spiral from the sugar in the wine as fuel.

For insulation tests, on HV transformers and motors I used an AM radio to listen for Partial Discharge (PD) a common method to detect the invisible spikes of contaminants creating a tick-tick sound in a quiet band. The tick rate increases rapidly with contamination and potential to breakdown.