Some questions about buying a used fluke 87 III/V

[M. András]

checked my 289 for curiosity, the 400ma socket reads 9.998/9k, the 10 amp socket reads 0.08ohm

[eevblogfan]

mine 287 was flikering between 9,998~7 . so I posted here 9,997  

[alm]

BTW , if the resistance of the percsision resistor changes via the tem'p  , canno't we compenset that via thermistor/thermo couple ? (IE , define that every 0.1C = 0.02ppm to add  or something like this ..)

This trick is used by TCXOs (temperature compensated crystal oscillators). Sometimes components with an opposite tempco are used in series to decrease the net tempco. The trouble with sensing the shunt resistor temperature is that you need to measure the resistor temperature accurately. Since the resistor is dissipating power, its core will always be hotter than its case. You could model this with the thermal resistance, but it's probably more trouble than it's worth, a more expensive resistor with a lower tempco is probably cheaper. Putting the shunt resistor in an oil bath appears to be more common, but is not very practical in a handheld meter.

[jonsig]

Sorry about resurrecting this interesting thread . But i cant seem to find the date of manufacture for the 87-series 3 .
BTW mine reads 1003 ohms / 1002.8 in hi -res via µA socket.

[retiredcaps]

But i cant seem to find the date of manufacture for the 87-series 3 .

User manual has a copyright date of Oct 1997 suggesting the first III series was likely introduced sometime in 1997.

[retiredcaps]

Teardown pictures of the 87 III at

https://www.eevblog.com/forum/testgear/fluke-87-iii-pictures!/

suggest year 1998 week 14 on the main IC supporting the theory that the manual dated Oct 1997 is likely correct.

[jonsig]

Sorry , but its a problem with your link .

Yeah i read that 87 -3 switched background light in the meantime . First 87-3 models had green ,battery destroying back light .My unit has blue-white´ish  back light . Wonder if it´s late model .

[mos6502]

Yeah i read that 87 -3 switched background light in the meantime . First 87-3 models had green ,battery destroying back light.

Wait, what? Can anyone elaborate on this? Why is it battery destroying?

I just checked the 87-III service manual, and it only mentions "Backlight, White" in the parts list ...

FYI, my 87-V (manufactured in 2014) reads 1.0015.

[ericloewe]

Yeah i read that 87 -3 switched background light in the meantime . First 87-3 models had green ,battery destroying back light.

Wait, what? Can anyone elaborate on this? Why is it battery destroying?

Presumably because it uses a crapton of power.

[retiredcaps]

Yeah i read that 87 -3 switched background light in the meantime . First 87-3 models had green ,battery destroying back light.

Wait, what? Can anyone elaborate on this? Why is it battery destroying?

I just checked the 87-III service manual, and it only mentions "Backlight, White" in the parts list ...

FYI, my 87-V (manufactured in 2014) reads 1.0015.

Earlier/inital versions of the 87 III used a green colored backlight.  Later versions switched to a white backlight which reduced battery consumption.

[mos6502]

Yeah i read that 87 -3 switched background light in the meantime . First 87-3 models had green ,battery destroying back light.

Wait, what? Can anyone elaborate on this? Why is it battery destroying?

I just checked the 87-III service manual, and it only mentions "Backlight, White" in the parts list ...

FYI, my 87-V (manufactured in 2014) reads 1.0015.

Earlier/inital versions of the 87 III used a green colored backlight.  Later versions switched to a white backlight which reduced battery consumption.

OK, but why? A green LED doesn't draw much more power than a white LED. Or is the green Fluke backlight EL based?

I bought an 87-III that is due to arrive today ... interestingly the photos in the listing didn't show the backlight. 

[retiredcaps]

OK, but why?

Ebay seller a-fluke, had a listing, that described the difference between the two and why?  I don't see a listing from him at this moment.

I can't test because I don't have a 87 III.

[mos6502]

OK, but why?

Ebay seller a-fluke, had a listing, that described the difference between the two and why?  I don't see a listing from him at this moment.

I can't test because I don't have a 87 III.

<google-fu> You mean this guy?

http://stores.ebay.com/Multimeters-and-Accessories

I found this listing:

http://www.ebay.com/itm/Fluke-87-88-Multimeter-WHITE-LED-Back-Light-Upgrade-Conversion-Module-Kit-/371548347489?hash=item568201dc61

He claims the green backlight is incandescent? Whaaat? That makes no sense. The 87-III is from when, the late 90s/early 2000s? Green LEDs were around then. In fact much earlier. It would make zero sense for Fluke to use incandescent bulbs. Also, in his photo, you can see that the backlight consists of four light sources. If they used light bulbs, they wouldn't have used four of them. On top of that, an incandescent backlight wouldn't be green, unless they painted the bulbs green.

My meter is going to arrive in a few hours. If it has the green backlight, I'll do some current measurements, take it apart and check it out.

[mos6502]

So the 87-III just arrived. Too bad, it's a white backlight. By the way, it does NOT turn off automatically, just like on the 87V. It only has one brightness level, though (about as bright as the high level of the 87V). I also did the resistance check aginst the mA jack: 1.0012k.

[ModemHead]

This is an incandescent backlight module from an original 87 (circa 1990).  Sorry for the bad focus, I'm in a bit of a hurry here.  Not sure where the green color comes from, it's sealed up and I don't wish to break it.

It draws 60mA at 8.5V.

Edit:
To be honest, the only reason I called it incandescent is because I had it in a container labeled "old 87 incandescent backlight module".  I just did a quick test and it draws practically no current until a knee when the terminal voltage reaches 3.0V.  Which sounds more like there's actually some arrangement of LEDs on the other side.  In any case, it is a power hog.

[mos6502]

Thanks man, very interesting. Are you a-fluke on eBay?

Obviously it's 2x2 green LEDs in series at 30 mA each. You could probably replace those 130 ohm resistors with 1k ones and it would still be bright enough. Do you know if the models with the green backlight have a backlight timer?

One downside I found is that the 87-III doesn't sound the beeper in diode test mode. Bummer.

The different bargraph types of the 87-III vs the 87-V are also curious ...

[ModemHead]

Thanks man, very interesting. Are you a-fluke on eBay?

Nope, not a-fluke. Although I did get a new backlight module from him for my old 87 a few years ago, and that's probably the reason I labeled the old one "incandescent" when I stored it away. 

My original 87 has a 60-second backlight timer. And annoyingly, you can only turn it on with the button. The whole meter has to be turned off to get the backlight off early.

And yes, those resistors are wasting a ridiculous amount of power.

[Wytnucls]

The Fluke 185 has a similar green backlight consisting of 7 LEDs, with one, mercifully, left unpopulated.
Current draw goes from 16mA to 160mA, with the green backlight ON (2 AA batteries).

[mos6502]

Alright, I recently got a Fluke 88 (original series, with green backlight) and I wanted to get to the bottom of this. I measured the battery drain. Here are my findings:

	Fluke 88 (green BL)	Fluke 87 III (white BL)	Fluke 87 V (white BL)
off	9.6µA	8.6µA	0.1µA
VDC	760µA	920µA	1.15mA
VDC, BL on	22mA	26mA	9.18mA (Level 1), 21.2mA (Level 2)

So much for "battery destroying". Another myth busted. Plus, the green actually looks cooler.

Edit: added data for 87 V.

No idea if the larger off-state drain of the older meters is due to aging (carbon from the switch causing leakage current) or due to the circuit design. IMHO it must be the latter, because all 3 meters measure within 2 counts of each other (quick check with a 9V battery: 87 V says 9.033, 87 III says 9.031, 88 says 9.032) , I think internal current leaks would have an effect on the calibration.

Edit 2: ah, found it. The older 80 series have a signal called PDS (power down signal) that is connected to VBT+ and in the off state is pulled down to VBT- through a 1M resistor. So all the older 80 series will have an off state drain of around 9 microamps. It's all good.

[BMack]

Thanks man, very interesting. Are you a-fluke on eBay?

Obviously it's 2x2 green LEDs in series at 30 mA each. You could probably replace those 130 ohm resistors with 1k ones and it would still be bright enough. Do you know if the models with the green backlight have a backlight timer?

One downside I found is that the 87-III doesn't sound the beeper in diode test mode. Bummer.

The different bargraph types of the 87-III vs the 87-V are also curious ...

I didn't know about this before I bought it either...so I bought another 87V and eventually I'll be getting around to listing the 87 III, not just for that but another knock(don't like the holster, capacitance, temp) it's harder than I thought to adjust to the limited feature set.

In some light I do like the green light more but most of the time I prefer the white. At least it isn't orange like Agilent/Keysight, that is soo weird to me.

[mos6502]

The 87 III does have some features that the 87 V is missing. The autoranging is much faster. But the main thing is, the 87 III's bar graph (actually an analog pointer) has 6 times the resolution of the 87 V's bar graph (1000 counts full scale vs. 6000 counts full scale). I'll keep mine for that reason alone.

In the original 80 series, the 83, 87 and 88 all had different LCDs. The 83 had a regular bar graph that is just a full scale reading of the current range. The 87 had the high resolution analog pointer (4000 counts, wrapping four times for each range). The 88 had yet another type, a 2000 count analog pointer, wrapping twice per range. So the high res pointer was actually a big feature that distinguished the 87 from the cheaper 83.

Probably to save money in production, on the 80 V series, the 83 V, the 87 V and the 88 V all use the same LCD. So you only get the regular 6000 count bar graph.