Ahh huh...just touched the voltage cal pot...it jumped big jump back to 9.99...volts on 10V in.
Now varying the wiper up/dwn it appears ok and changes accordingly (linear fashion) but at first it jumped ....a lot. Possible pot issue?
Ahh huh...just touched the voltage cal pot...it jumped big jump back to 9.99...volts on 10V in.
Now varying the wiper up/dwn it appears ok and changes accordingly (linear fashion) but at first it jumped ....a lot. Possible pot issue?
Have a look at the solder joints holding it to the board before blaming the pot.
Ahh huh...just touched the voltage cal pot...it jumped big jump back to 9.99...volts on 10V in.
Now varying the wiper up/dwn it appears ok and changes accordingly (linear fashion) but at first it jumped ....a lot. Possible pot issue?
Have a look at the solder joints holding it to the board before blaming the pot.
+1, most of the cases I found are cold joins, just watch carefully if the solder is shiny or hazy (cold join).
Many thanks gents....took it apart touched up solder joins. They look ok under 3X loupe but they are shiner with 63/37 solder. It appears ok now, wiggling the pot before doing the joints didn't make any change but as said I redid them anyway.
Oh had a scare....put it back together temporarily held battery on meter...no display...re-did this all another 2 times...then realised the elastometric carbon strip was not clamped down by the PCB screws...urrrgh!
Ahh huh...just touched the voltage cal pot...it jumped big jump back to 9.99...volts on 10V in.
Now varying the wiper up/dwn it appears ok and changes accordingly (linear fashion) but at first it jumped ....a lot. Possible pot issue?
Have a look at the solder joints holding it to the board before blaming the pot.
+1, most of the cases I found are cold joins, just watch carefully if the solder is shiny or hazy (cold join).
It's all shit lead free solder which is not shiny...
Many thanks to all. I had noticed the meter getting really bad on accuracy in volts since the autumn cold weather arrived.
I fired it up this morning...spot on accuracy.
I'm not a meter man...I just use them.... they work or I get Peeved off! Once again thanks she's all good now.
Hmmm its a $6 IC in Aust. Going to have to look at this. Noticed they have this IC in .1% and .05%! But the .05% is ~$6.
I'm not a meter man...but hey I'll try anything once....well almost anything! Had to laugh...typing in LT 1970 into browser ( I mistakenly left a space between terms) found "Mutiny on the Bounty"! What's that....your multimeter is not accurate...your going to modify it...Mutiny I say
I'll look at this and get back. Thanks
Hmmm its a $6 IC in Aust. Going to have to look at this. Noticed they have this IC in .1% and .05%! But the .05% is ~$6.
and that's probably why it was not fitted - that's a lot of money in china!
Hmmm its a $6 IC in Aust. Going to have to look at this. Noticed they have this IC in .1% and .05%! But the .05% is ~$6.
and that's probably why it was not fitted - that's a lot of money in china!
nah, they buy used fake ones on the black market...
Just a question...modifying the Vref to an LT1790 hi precision...they don't explain (in the part pdf or above site) if they use 1% or better resistors and high precision caps?
I guess at least 1% would be required...or is this overkill.
They won't prevent the meter from exploding in your hand if you select the wrong range.
That's why we don't use meters with possible low impedance path on high energy circuits unless we check twice or more we're on right range. No HRC fuse or CAT rating will help even on low voltage distribution line if you're near the transformer and something goes really wrong - I put my safety into considerations about other, more probable things, like knowing that if something goes wrong I won't fall down from the pole and have a head trauma (most electricity injures come not from an actual eletrical shock, but blunt trauma after you did nasty landing fom the ladder/whatever).
c) Joe has exploded several meters in his thread. He doesn't test on the current ranges.
And working at a substation 15kV -> 400V I haven't exploded any.
Would you use a UT61E if you were working around substations every day?
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Yes, I would, to check why the light is out in the building. No other reason to use a multimeter in that environment;) Other things are measured via current transfomers and so on connected to separate meters so no reason or need to poke around. I must admit, it' s a bad example;)
But there is a device that will make most CAT focused people cringe. Incandescent bulb with two probes attached. It's still very useful - RCD tester, phase to earth voltage checker or phase-to-phase (you have to do it quick, as eg 230V bulbs don't like 400V for a long ime) and it loads the circuit well enough to get rid of any ghost voltages that LoZ option on DMM won't cover. I'm yet to see voltage stick that will draw 100W or so.
Just a question...modifying the Vref to an LT1790 hi precision...they don't explain (in the part pdf or above site) if they use 1% or better resistors and high precision caps?
I guess at least 1% would be required...or is this overkill.
For most people, a DMM is only used in an indoor environment where temperature is in a narrow range. Therefore, tempco can be ignored. In that case, 1% or 10% doesn't make any difference if there is a trimming pot.
Is that based on your personal experience of the entire world population of handheld meters? I will say that I have never taken my 34401 into the field, but for handhelds I would guess until recently the vast majority of the time the meter is used outside the house. It gets a fair amount of heat cycling in the trailer and garage. Still, I don't need anything much beyond the free meters from Harbor Freight for this work so temperature is little concern. If they had a backlight and temperature input, I would be golden...
blueskull...it gets quite cold (down to 0ºC and below) and hot (40ºC) here. Used indoors home work area, temp is around 15ºC ~ 25ºC.
Really if its accurate to .01Volt on low range then I'm happy. ATM its behaving much better since I re-worked the pot joins. If it stays this way then I'll probably leave it.
I tested my UNI-T 61E between 20°C and 36°C by leaving it on in a PS foam box with a incandescent lamp for a few hours, connecting it to an external voltage reference
In spite of what I expected the value displayed never changed, although it was lower than the value displayed by a better multimeter
I tried to calibrate it via the inner voltage calibration trimmer and realized it is real crap
if you turn it 360° there is no change
then another few degrees of rotation and the value suddenly changes a lot
I should replace it with a new bourns trimmer
I just wonder if the crappy trimmer variation with temperature casually compensates the variation of the multimeter reference
......I tried to calibrate it via the inner voltage calibration trimmer and realized it is real crap ...if you turn it 360° there is no change..then another few degrees of rotation and the value suddenly changes a lot
I should replace it with a new bourns trimmer
That is exactly what I initially saw. Then winding the pot back and fourth...it started to give a more linear response. Quite odd like the wiper was stuck or not tracking correctly. Its keeping better voltage accuracy now though.
I also noted my PCB layout is different to the PCB in the Vref mod. The layout on mine is different and there is no unused pads for an LT1790 etc
The Pot on mine is "X202" so a 2K ohm pot multi-turn. The cct diagrams show it to be 1K ohm
That is exactly what I initially saw. Then winding the pot back and fourth...it started to give a more linear response. Quite odd like the wiper was stuck or not tracking correctly. Its keeping better voltage accuracy now though.
Those trimmers use a really, really soft carbon for the track. The wipers gunk up fast.
(they're usually only rated for 200 adjustments!)
I tested my UNI-T 61E between 20°C and 36°C by leaving it on in a PS foam box with a incandescent lamp for a few hours, connecting it to an external voltage reference
In spite of what I expected the value displayed never changed, although it was lower than the value displayed by a better multimeter
I tried to calibrate it via the inner voltage calibration trimmer and realized it is real crap
if you turn it 360° there is no change
then another few degrees of rotation and the value suddenly changes a lot
I should replace it with a new bourns trimmer
I just wonder if the crappy trimmer variation with temperature casually compensates the variation of the multimeter reference
I would expect for 16 degree you would see 5.125 uV/degC or 82uV. Basically 8 counts. For all I know you were in the DCV range. I did not save my data and tc may not be linear. After temperature compensating mine with a diode/resistor, tc was 0.625uV/degC.
I also noted my PCB layout is different to the PCB in the Vref mod. The layout on mine is different and there is no unused pads for an LT1790 etc
damn, i have to check mine later!!
......I tried to calibrate it via the inner voltage calibration trimmer and realized it is real crap ...if you turn it 360° there is no change..then another few degrees of rotation and the value suddenly changes a lot
I should replace it with a new bourns trimmer
That is exactly what I initially saw. Then winding the pot back and fourth...it started to give a more linear response. Quite odd like the wiper was stuck or not tracking correctly. Its keeping better voltage accuracy now though.
I also noted my PCB layout is different to the PCB in the Vref mod. The layout on mine is different and there is no unused pads for an LT1790 etc
The Pot on mine is "X202" so a 2K ohm pot multi-turn. The cct diagrams show it to be 1K ohm
mine is 2kohm too
I made as you advised and was able to trim it closer to (what is supposed to be) the real voltage
now it is still low on ohm reading but anyway I have better multimeters for that purpose
I tested my UNI-T 61E between 20°C and 36°C by leaving it on in a PS foam box with a incandescent lamp for a few hours, connecting it to an external voltage reference
In spite of what I expected the value displayed never changed, although it was lower than the value displayed by a better multimeter
I tried to calibrate it via the inner voltage calibration trimmer and realized it is real crap
if you turn it 360° there is no change
then another few degrees of rotation and the value suddenly changes a lot
I should replace it with a new bourns trimmer
I just wonder if the crappy trimmer variation with temperature casually compensates the variation of the multimeter reference
I would expect for 16 degree you would see 5.125 uV/degC or 82uV. Basically 8 counts. For all I know you were in the DCV range. I did not save my data and tc may not be linear. After temperature compensating mine with a diode/resistor, tc was 0.625uV/degC.
I guess I've just been lucky as I checked the multimeter reading various times during the test and it didn't show any variation apart flipping the last digit at the end
I used a seasoned AD588BQ V reference with 0.1% 15ppm resistors to bring the voltage down around 1.5V
so I think the variation is no more than 1 part per 10000 over 20 to 35°C
of course I cannot say anything about drift in other voltage ranges
BTW during that time I've also checked the 1.5V reference (both the reference and the other DMM at ambient temperature) with a Brymen 867S and it showed no drift
