Test Equipment Anonymous (TEA) group therapy thread

[bd139]

One of you lovely people wouldn't happen to know where to get a few button caps for this series?

https://www.keysight.com/my/partDetail/E3630-40007

Phone up your local rep

Heh. I know they have a comprehensive spare part catalog but I never ordered from them, TBH.

They're fairly decent at it. UK at least you just phone the rep line and ask for them to raise an order for parts. They then get some woman in Spain to phone you back and take credit card details and the stuff turns up a couple of weeks later.

[mnementh]

One of you lovely people wouldn't happen to know where to get a few button caps for this series?

   https://www.amazon.com/Adafruit-Colorful-Square-Tactile-Assortment/dp/B00KLDQ0YG

Those look suspiciously similar to caps for these 12mm x 12mm jumbo tactile switches, which I just recently got a handful of in an Ardu sensor kit. The cap measures 10mm x 10mm, fits standard snap-off 3.8mm square shaft, with 3.25mm shell depth/6.35mm overall depth. Front offset (thickness of front layer to top of switch post) is 1mm, so 2.25mm depth from tip of switch shaft to bottom edge of outer square cap once installed. If yours are 10mm x 10mm and that is sufficient depth, seems your cheapest/quickest solution (as these are available via Amazon Prime at those prices), plus you get a handful of jumbo tactiles to play with elsewhere.

https://www.amazon.com/uxcell-Plastic-12x12mm-Pushbutton-12x12x7-3mm/dp/B07PK3W4XL

https://www.amazon.com/uxcell-Plastic-12x12mm-Pushbutton-12x12x7-3mm/dp/B07PHYNRNT

https://www.amazon.com/uxcell-Plastic-12x12mm-Pushbutton-12x12x7-3mm/dp/B07PFPH32Z

UXCELL also sells similar caps in multiple colors for ~$5/20, but they advertise them as 12mm x 12mm. These are also available with clear covercaps so you can make custom keys which DO measure 12mm x 12mm (they're used on my mental defective kit calculator); so the listings may or may not be in error.



EDIT: Looking at these photos from the UXCELL listing, probably are actually 12mm x 12mm; the outer walls of the switch look thicker.

mnem
 

[tautech]

I'm talking about the voltage ref because tautech mentioned previously that the ref in the SDM was potentially drifting a little bit. See quote bellow.

It will be automated using a universal calibrator with a PC running a cal script but it's been reported SDM's drift a little until their references become suitably aged and stable so the user cal process has been developed for owners with decent references to make fine adjustments to accuracy.

Defpom tweaked his 3065X using one of IanJ's references that have been calibrated with a 8.5 digit DMM.
AFAIK it worked out just fine even though the adjustment process was still in the beta stages and Defpom provided some feedback to Siglent for them to polish it some.

Yes that was in reference to a post made mid last year by a SDM3065X owner which uses the LM399 ref:

If you find an old datasheet for the LM1/2/399; the drift matched a fresh (not burned in) LM399 rather precisely.

I highly suspect that while SDM3055 uses a different reference they also are un-aged and drift close to datasheet spec hence why Siglent have developed an adjustment process however I don't agree with their insistence for it to remain from the public domain.   

[tggzzz]

There is NO compensation for circuit loading in any of these meters. They measure what appears at the terminals regardless of the load they place on the external voltage. The meters are in parallel so differences in input impedance is irrelevent. The impedance should not matter with a modern Voltage standard anyway because it's imedance is tiny compared to the meter.

It is reasonable to expect that a 10Mohm load would load the output of a reference voltage source sufficiently to be detected by a decent meter, given a appropriate definition of "decent".

[mnementh]

Nope. Not gonna get sucked into another argument here. Bottom line is that for as long as we've been trying to measure angry pixies, different manufacturers' meters will give different readings from the same precision source.

Every meter is itself a series-parallel circuit, and as such will affect the measurement, and different designs affect it differently. Compounding that with modern meters is that they are subject to software flaws as well.

med's meter isn't in the realm of counting the individual electrons, but it is skirting around the edges of proper volt-nuttery.

mnem
 

[ch_scr]

Today I had to service my Keithley 2100 (aka "fake" Keithley as these are just an Array M3500A rebadger).
In fact I have serviced this device in the past - the electrolytics had given out (on a 2012 device - go figure).
But this time I noticed my resistance measurement going flaky - presumably the banana jacks.
Upon opening the device I noticed two things:
- one of the formerly changed capacitors had bulged its top (again)
- I could not seem to get good access to the banana jack block or immediately notice a problem
So I begrudgingly proceeded to take the device apart. Upon finishing the removal of the PCB from the device (it was not too bad really)
and closer inspection I again noticed two things:
- the deceased capacitor seemed to be installed by me with reversed polarity
- the problem with the banana jack block seemed to be one solder joint on the pcb - both things accessible without removing the pcb
What more is there to say - the device is back together and seems to work again. 

[mnementh]

Nobody in here has ever done either of those things... nuh-uhhhh!!!!

mnem
 

[Robert763]

There is NO compensation for circuit loading in any of these meters. They measure what appears at the terminals regardless of the load they place on the external voltage. The meters are in parallel so differences in input impedance is irrelevent. The impedance should not matter with a modern Voltage standard anyway because it's imedance is tiny compared to the meter.

It is reasonable to expect that a 10Mohm load would load the output of a reference voltage source sufficiently to be detected by a decent meter, given a appropriate definition of "decent".

Detected? Maybe if you have an 8.5 digit meter.
The reference used was a AD584 (not the best). Its output load regulation is 50ppm per mA maximum. A 10M load is 1uA load change at maxium 10V output  so 0.05ppm change. Thats 0.5uV MAXIMUM so 9.9999995V reading for 10V nominal.
The HP 735A was mentioned as being affected by a 10M load. That is correct it will be out by about 100ppm (100uV). This is because it has a resistive divider output of a several hundred ohms imepance and no freedback.
Mnementh is yet again making  statements and then saying something else when called on it.....

[Specmaster]

There is NO compensation for circuit loading in any of these meters. They measure what appears at the terminals regardless of the load they place on the external voltage. The meters are in parallel so differences in input impedance is irrelevent. The impedance should not matter with a modern Voltage standard anyway because it's imedance is tiny compared to the meter.

It is reasonable to expect that a 10Mohm load would load the output of a reference voltage source sufficiently to be detected by a decent meter, given a appropriate definition of "decent".

Disagree, if you connect a DMM with a 10Mohm loading in parallel with another DMM with say 10Gohm loading to a voltage source then its perfectly reasonable and logical to expect that both meters should (assuming identical calibration status) read the same, but they don't. If you do the same with a resistor, however then they will read differently as both DMM's are outputting a voltage which will differ and also both DMM's are also trying to measure the others impedance.

[tggzzz]

Nope. Not gonna get sucked into another argument here. Bottom line is that for as long as we've been trying to measure angry pixies, different manufacturers' meters will give different readings from the same precision source.

Every meter is itself a series-parallel circuit, and as such will affect the measurement, and different designs affect it differently. Compounding that with modern meters is that they are subject to software flaws as well.

It is nothing to do with different manufacturers. Different meters of the same type will give different readings, within the limits specified.

Meters are modeled as a perfect voltmeter that takes no current in parallel with a resistor. A precision Meyer should have a resistance of many Gohms. For many handheld meters that resistance is nominally 10Mohm, andthat is also the case for many precision meters on ranges >10V.

[tggzzz]

There is NO compensation for circuit loading in any of these meters. They measure what appears at the terminals regardless of the load they place on the external voltage. The meters are in parallel so differences in input impedance is irrelevent. The impedance should not matter with a modern Voltage standard anyway because it's imedance is tiny compared to the meter.

It is reasonable to expect that a 10Mohm load would load the output of a reference voltage source sufficiently to be detected by a decent meter, given a appropriate definition of "decent".

Disagree, if you connect a DMM with a 10Mohm loading in parallel with another DMM with say 10Gohm loading to a voltage source then its perfectly reasonable and logical to expect that both meters should (assuming identical calibration status) read the same, but they don't. If you do the same with a resistor, however then they will read differently as both DMM's are outputting a voltage which will differ and also both DMM's are also trying to measure the others impedance.

What do you mean by DMMs outputting a voltage?

[tggzzz]

There is NO compensation for circuit loading in any of these meters. They measure what appears at the terminals regardless of the load they place on the external voltage. The meters are in parallel so differences in input impedance is irrelevent. The impedance should not matter with a modern Voltage standard anyway because it's imedance is tiny compared to the meter.

It is reasonable to expect that a 10Mohm load would load the output of a reference voltage source sufficiently to be detected by a decent meter, given a appropriate definition of "decent".

Detected? Maybe if you have an 8.5 digit meter.
The reference used was a AD584 (not the best). Its output load regulation is 50ppm per mA maximum. A 10M load is 1uA load change at maxium 10V output  so 0.05ppm change. Thats 0.5uV MAXIMUM so 9.9999995V reading for 10V nominal.
The HP 735A was mentioned as being affected by a 10M load. That is correct it will be out by about 100ppm (100uV). This is because it has a resistive divider output of a several hundred ohms imepance and no freedback.
Mnementh is yet again making  statements and then saying something else when called on it.....

Yes to all of that!

[ch_scr]

There is NO compensation for circuit loading in any of these meters. They measure what appears at the terminals regardless of the load they place on the external voltage. The meters are in parallel so differences in input impedance is irrelevent. The impedance should not matter with a modern Voltage standard anyway because it's imedance is tiny compared to the meter.

It is reasonable to expect that a 10Mohm load would load the output of a reference voltage source sufficiently to be detected by a decent meter, given a appropriate definition of "decent".

Disagree, if you connect a DMM with a 10Mohm loading in parallel with another DMM with say 10Gohm loading to a voltage source then its perfectly reasonable and logical to expect that both meters should (assuming identical calibration status) read the same, but they don't. If you do the same with a resistor, however then they will read differently as both DMM's are outputting a voltage which will differ and also both DMM's are also trying to measure the others impedance.

What do you mean by DMMs outputting a voltage?

Propably meant to say it outputs a current

[Cerebus]

There is NO compensation for circuit loading in any of these meters. They measure what appears at the terminals regardless of the load they place on the external voltage. The meters are in parallel so differences in input impedance is irrelevent. The impedance should not matter with a modern Voltage standard anyway because it's imedance is tiny compared to the meter.

It is reasonable to expect that a 10Mohm load would load the output of a reference voltage source sufficiently to be detected by a decent meter, given a appropriate definition of "decent".

Well, we can be quite precise here as we know we're dealing with an AD584 set for 10V output. The AD584 has a worst case load regulation of 50 ppm/mA (typ 20 ppm/mA) for loads 0 < I_out < 5mA. So, 10M load on 10V => 1uA current => 50 ppb shift due to load regulation or 500 nV which means you'd need to be in \$8\frac{1}{2}\$ digit meter territory to measure the change due to loading.

[Specmaster]

There is NO compensation for circuit loading in any of these meters. They measure what appears at the terminals regardless of the load they place on the external voltage. The meters are in parallel so differences in input impedance is irrelevent. The impedance should not matter with a modern Voltage standard anyway because it's imedance is tiny compared to the meter.

It is reasonable to expect that a 10Mohm load would load the output of a reference voltage source sufficiently to be detected by a decent meter, given a appropriate definition of "decent".

Disagree, if you connect a DMM with a 10Mohm loading in parallel with another DMM with say 10Gohm loading to a voltage source then its perfectly reasonable and logical to expect that both meters should (assuming identical calibration status) read the same, but they don't. If you do the same with a resistor, however then they will read differently as both DMM's are outputting a voltage which will differ and also both DMM's are also trying to measure the others impedance.

What do you mean by DMMs outputting a voltage?

Perfectly simple, even with a analogue meter, remove the battery, no resistance ranges, but it will still measure a voltage if one is applied to it. If a DMM does not output a voltage then it cannot measure the resistance that you wish to measure as there is zero current flowing though the circuit for the meter to derive a value of the unknown resistor from.

[Robert763]

There is NO compensation for circuit loading in any of these meters. They measure what appears at the terminals regardless of the load they place on the external voltage. The meters are in parallel so differences in input impedance is irrelevent. The impedance should not matter with a modern Voltage standard anyway because it's imedance is tiny compared to the meter.

It is reasonable to expect that a 10Mohm load would load the output of a reference voltage source sufficiently to be detected by a decent meter, given a appropriate definition of "decent".

Well, we can be quite precise here as we know we're dealing with an AD584 set for 10V output. The AD584 has a worst case load regulation of 50 ppm/mA (typ 20 ppm/mA) for loads 0 < I_out < 5mA. So, 10M load on 10V => 1uA current => 50 ppb shift due to load regulation or 500 nV which means you'd need to be in \$8\frac{1}{2}\$ digit meter territory to measure the change due to loading.

Two independent calcualtions giving same result!

[Specmaster]

There is NO compensation for circuit loading in any of these meters. They measure what appears at the terminals regardless of the load they place on the external voltage. The meters are in parallel so differences in input impedance is irrelevent. The impedance should not matter with a modern Voltage standard anyway because it's imedance is tiny compared to the meter.

It is reasonable to expect that a 10Mohm load would load the output of a reference voltage source sufficiently to be detected by a decent meter, given a appropriate definition of "decent".

Disagree, if you connect a DMM with a 10Mohm loading in parallel with another DMM with say 10Gohm loading to a voltage source then its perfectly reasonable and logical to expect that both meters should (assuming identical calibration status) read the same, but they don't. If you do the same with a resistor, however then they will read differently as both DMM's are outputting a voltage which will differ and also both DMM's are also trying to measure the others impedance.

What do you mean by DMMs outputting a voltage?

Propably meant to say it outputs a current

Agreed, but behind that current is a measurable voltage, which can be measured via another meter switched to V mode, while the other meter is switched to    mode. If that was not true, then there would not be a current, its basic ohms law.

[ch_scr]

There is NO compensation for circuit loading in any of these meters. They measure what appears at the terminals regardless of the load they place on the external voltage. The meters are in parallel so differences in input impedance is irrelevent. The impedance should not matter with a modern Voltage standard anyway because it's imedance is tiny compared to the meter.

It is reasonable to expect that a 10Mohm load would load the output of a reference voltage source sufficiently to be detected by a decent meter, given a appropriate definition of "decent".

Disagree, if you connect a DMM with a 10Mohm loading in parallel with another DMM with say 10Gohm loading to a voltage source then its perfectly reasonable and logical to expect that both meters should (assuming identical calibration status) read the same, but they don't. If you do the same with a resistor, however then they will read differently as both DMM's are outputting a voltage which will differ and also both DMM's are also trying to measure the others impedance.

What do you mean by DMMs outputting a voltage?

Propably meant to say it outputs a current

Agreed, but behind that current is a measurable voltage, which can be measured via another meter switched to V mode, while the other meter is switched to    mode. If that was true, then there would not be a current, its basic ohms law.

While technically correct, what is regulated is the current, the compliance voltage voltage is variable but the current is not (it usually varies with selected resistance range tho).
And while there always is a voltage and a current together (carefully trying to avoid opening another can of worms here ) what is usually referred to is the regulated element.
EDIT: Now I'm really curios if someone manages to whip out a multimeter that does it with constant voltage

[Cerebus]

Two independent calcualtions giving same result!

It's so trivial that calling it a "calculation" almost seems like unnecessarily glamourising it. 

[Cerebus]

While technically correct, what is regulated is the current, the compliance voltage voltage is variable but the current is not (it usually varies with selected resistance range tho).
And while there always is a voltage and a current together (carefully trying to avoid opening another can of worms here ) what is usually referred to is the regulated element.
EDIT: Now I'm really curios if someone manages to whip out a multimeter that does it with constant voltage

I have seen meters that use a fixed constant voltage source with a calibrated resistor in series as the current source for the ohms range. I'm reasonably confident that I've seen a pure constant voltage source for a resistance range (effectively using a current range to make the measurement), but I'd be hard pressed to name the meter or series of meters that i saw it in.

[Specmaster]

There is NO compensation for circuit loading in any of these meters. They measure what appears at the terminals regardless of the load they place on the external voltage. The meters are in parallel so differences in input impedance is irrelevent. The impedance should not matter with a modern Voltage standard anyway because it's imedance is tiny compared to the meter.

It is reasonable to expect that a 10Mohm load would load the output of a reference voltage source sufficiently to be detected by a decent meter, given a appropriate definition of "decent".

Disagree, if you connect a DMM with a 10Mohm loading in parallel with another DMM with say 10Gohm loading to a voltage source then its perfectly reasonable and logical to expect that both meters should (assuming identical calibration status) read the same, but they don't. If you do the same with a resistor, however then they will read differently as both DMM's are outputting a voltage which will differ and also both DMM's are also trying to measure the others impedance.

What do you mean by DMMs outputting a voltage?

Propably meant to say it outputs a current

Agreed, but behind that current is a measurable voltage, which can be measured via another meter switched to V mode, while the other meter is switched to    mode. If that was true, then there would not be a current, its basic ohms law.

While technically correct, what is regulated is the current, the compliance voltage voltage is variable but the current is not (it usually varies with selected resistance range tho).
And while there always is a voltage and a current together (carefully trying to avoid opening another can of worms here ) what is usually referred to is the regulated element.

Yes, exactly that, 1,000 times, I may not have phrased it correctly, but it is a measurable voltage just the same at the + and - input terminals of the meter doing the resistance check. That voltage value will vary according to make and model, hence why some can drive white and or a blue LED while others can only drive a red, green or yellow LED. The actual output voltage in resistance mode is not that critical, as the manufacturer will know this and will compensate for it on an individual meter by meter basis, called calibration.

[Robert763]

There is NO compensation for circuit loading in any of these meters. They measure what appears at the terminals regardless of the load they place on the external voltage. The meters are in parallel so differences in input impedance is irrelevent. The impedance should not matter with a modern Voltage standard anyway because it's imedance is tiny compared to the meter.

It is reasonable to expect that a 10Mohm load would load the output of a reference voltage source sufficiently to be detected by a decent meter, given a appropriate definition of "decent".

Disagree, if you connect a DMM with a 10Mohm loading in parallel with another DMM with say 10Gohm loading to a voltage source then its perfectly reasonable and logical to expect that both meters should (assuming identical calibration status) read the same, but they don't. If you do the same with a resistor, however then they will read differently as both DMM's are outputting a voltage which will differ and also both DMM's are also trying to measure the others impedance.

What do you mean by DMMs outputting a voltage?

Propably meant to say it outputs a current

Agreed, but behind that current is a measurable voltage, which can be measured via another meter switched to V mode, while the other meter is switched to    mode. If that was true, then there would not be a current, its basic ohms law.

While technically correct, what is regulated is the current, the compliance voltage voltage is variable but the current is not (it usually varies with selected resistance range tho).
And while there always is a voltage and a current together (carefully trying to avoid opening another can of worms here ) what is usually referred to is the regulated element.
EDIT: Now I'm really curios if someone manages to whip out a multimeter that does it with constant voltage

Not a multimeter, but this one pictured. It uses a 2V lead acid cell and while the current is limited it is not regulated. Both the voltage across and current through the resistor being measured change with it's value.
The instument has a ratiometric movement with two coils, one responding to roltage and the other (opposing it) to current.
This technique is also used in bonding testers. A simple low ohmmeter can be made with DPM module in ratiometric mode and a a low resistance (ammeter shunt is good) in series with a current limited supply (1.2V recharagable and 1R resistor will give a ~ 1A test current)

[Robert763]

While technically correct, what is regulated is the current, the compliance voltage voltage is variable but the current is not (it usually varies with selected resistance range tho).
And while there always is a voltage and a current together (carefully trying to avoid opening another can of worms here ) what is usually referred to is the regulated element.
EDIT: Now I'm really curios if someone manages to whip out a multimeter that does it with constant voltage

I have seen meters that use a fixed constant voltage source with a calibrated resistor in series as the current source for the ohms range. I'm reasonably confident that I've seen a pure constant voltage source for a resistance range (effectively using a current range to make the measurement), but I'd be hard pressed to name the meter or series of meters that i saw it in.

I can MEGGER They have to use a constant voltage.
Edit or more like a DMM Fluke 1507 50,100,250, 500 or 1000V

[ch_scr]

[...]
Yes, exactly that, 1,000 times, I may not have phrased it correctly, but it is a measurable voltage just the same at the + and - input terminals of the meter doing the resistance check. That voltage value will vary according to make and model, hence why some can drive white and or a blue LED while others can only drive a red, green or yellow LED. The actual output voltage in resistance mode is not that critical, as the manufacturer will know this and will compensate for it on an individual meter by meter basis, called calibration.

What makes the Keithley 2100 particularly annoying is that it outputs way above what is needed to light up a blue led - but elects to measure said voltage in the 1.2V range. Such wasted potential, I think almost all people would trade the extra digit on the "usual diode" voltage drop measurement (which is highly temperature dependent anyway, making practicality of said digit...) with the convenience to measure leds & zeners up to almost 12V. 

[ch_scr]

I can MEGGER They have to use a constant voltage.

Not a multimeter, but this one pictured. It uses a 2V lead acid cell and while the current is limited it is not regulated. Both the voltage across and current through the resistor being measured change with it's value.
The instument has a ratiometric movement with two coils, one responding to roltage and the other (opposing it) to current.
This technique is also used in bonding testers. A simple low ohmmeter can be made with DPM module in ratiometric mode and a a low resistance (ammeter shunt is good) in series with a current limited supply (1.2V recharagable and 1R resistor will give a ~ 1A test current)

Both excellent examples of circumstances where doing it different means doing it right