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UT61E drift and recalibration

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Rick Law:
Ahem,  Just to close off my thoughts on UT61E and DMM Check Plus...

Taking advantage of a moment of lax of self discipline, I stumbled into the voltagestandard site quite by accident, (I was controlled by unknown alien presence at the time) and some how I managed to click BUY...

I promised myself that I will not exceed my entertainment budget and I just did - The alien control was so powerful that I even clicked the dual frequency option and enclosure option.  I will punish myself later for such lack of discipline.

Now that is really really silly.  I just spend $90+ to check on my $60 dmm.  You can now begin laughing at me.

I am well prepared with proper excuses:
Excuse 1 - I have 5 dmm's, I need to know which one is more wrong
Excuse 2 - with the dual frequency, I can use my $90 checker to check if my $70 cheap USB scope drawing different square waves
Excuse 3 - My next project is to do a "Tricorder", it should be able to measure anything.  I need something to validate the tricorder readings.
Excuse 4 - I didn't do it.  I was temporarily controlled by aliens taking over my clicking finger.

Now let me go kick myself for exceeding my self-imposed entertainment budget.  But I really like the idea that I can do a sanity check.  That my measurement is by some standard with certain percentage of some standard...

M0BSW:
 My experience with the 61E is also on resistance, I have  in a box a 5.7 ohm 1% resistor, my two Alpatek's  trusted meters read 5.7 dead on , however my 61e did read 5.7 now its drifted to 6.0 ohms , in a year. I would adjust it but have know ideal which pot to twiddle plus I'm not sure if 1.3 ohms is acceptable with the specs of the 61E.

Rick Law:

--- Quote from: M0BSW on November 27, 2013, 07:40:42 am --- My experience with the 61E is also on resistance, I have  in a box a 5.7 ohm 1% resistor, my two Alpatek's  trusted meters read 5.7 dead on , however my 61e did read 5.7 now its drifted to 6.0 ohms , in a year. I would adjust it but have know ideal which pot to twiddle plus I'm not sure if 1.3 ohms is acceptable with the specs of the 61E.

--- End quote ---

I found part of the problem is the probe and the socket doesn't make very good contacts.  I can twist the probe banana plug (as if it is a dial) and get +- 0.3ohm delta easily as I turn the plug like a dial.  Cleaning the contacts helps for a while.

I suspect if you clean the plugs, jiggle it, you may get 6.0 ohms back down to 5.7ohms.

stephenlm324:
I have recently purchased a UT61E and found that the stability could be better. I found some interesting information on an external Vref which deserves credit but I don't do Chinese. The link "http://forum.eepw.com.cn/thread/239953/1" has the required info to retro fit the UT61E with an external Vref LT1790. The temp co. is typ. 5ppm. as opposed to 75ppm in the ES51922. I can confirm the accuracy of this info as I have just completed the mod along with replacing the pot VR1 with a resistor network and a 50ohm pot. The standard is 2k and drifts 1% (20ohm) with vibration alone.
The mod requires the LT1790ACS6-1.25 two 10k resistors one 10uF cap all SMD. R15 needs to be removed and replaced in position R51.
My meter is already looking much more stable, I suspect the standard Vref warms up after switch on inside the main chip, taking some time to settle.

george graves:
^That's nice!  I think I'll wait for someone to do a English write up before I would give it a go!  :D

Since the 61E is a 22,000 count meter, would it be better to calibrate it at something just below 2.2 volts so that you get the full count on the meter?

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