Fluke 87V - DC output in Ohms range?

[tec5c]

Hi all,

I was fiddling around with 2 Fluke 87's (III and V models) at work today due to some down-time. I happened to notice that the 87 V has ~2.7v across the probes when in the ohms range. I was curious to know why this is the case. Compared to the 87 III model that only had ~0.6-0.7v across its probes in the ohms mode.

I couldn't find much info doing a Google search, other than the service manual but I haven't read through that thing just yet so I apologise if the answer to my question is in the manual/is quite obvious.


Cheers.

[alm]

Maybe it's related to the nS range that the 87V added? Better compliance of the current source could mean an increased resistance range, although the max range in resistance (as opposed to conductance) mode is essentially the same for both meters.

Note that the voltage open circuit voltage is probably higher than the voltage for most in-circuit measurements with a finite resistance. I would expect the voltage to remain below 0.4 V up to 1 MOhm or so.

[Robomeds]

I'm not sure but I will take a look when I get home to see if mine show the same.  The 87-III also has a nS range so I don't think that alone would explain it.

[jebcom]

I'll also have to check when I get home, but I wonder if this is shared with the diode test range. The higher potential will allow you test more types of LEDs. Sharing the circuit would allow them to economize on the design somewhat.

[jebcom]

I checked mine and the diode test is about 7.3V. That's the same as the 600, 6k, 60k ranges.
600k is about 3.5V. 6M is 5.3V. Other ranges are about 2.79V.

[IanB]

I would have hoped the voltage remained below ~0.6 V to facilitate in circuit resistance measurements. Maybe the 87V is not really an electronics meter, but more of an industrial meter?

[alm]

Is this open circuit or in an actual 600/6k/60k load? Open circuit is always going to be higher. In auto range it would up range until it would reach a range where the compliance was sufficient (or its highest range).

[jebcom]

the only load was the 10 meg multimeter input.
that seems to be what op was doing.

[kg4arn]

 My 87V is putting out a constant current on the 600 through 600K scales.
The current output on the 6M and 60M scales decreases with increasing measured resistance. 

Current was calculated by measuring the voltage across the test resistor with a RIGOL DM3068 in high impedance mode (>10G).
                                                                                                                           
 
Ohm Scale      Current           Max  V = scale * Current                  Test resistor
600                  1mA                             0.6V                                        99.2 ohm
6K                   100uA                          0.6V                                        983
60K                 10uA                            0.6V                                        9.87K
600K               1uA                              0.6V                                        98K


6M                   1uA                              0.9V measured                        990K
6M                   0.63uA                         3.9V measured                        6M
60M                 0.26uA                         2.6V measured                       10M
60M                 0.09uA                         4.5V measured                       50M
 

[SLJ]

Not home now to check but higher voltage could be for ability to test LEDs.  I remember before I bought mine one of the reoccurring comments was that the V had high enough voltage to test LEDs when others didn't.