| Electronics > Repair |
| 8846A Fluke DMM has a proplem with the reading and it shows as bellow |
| (1/2) > >> |
| Gen.Eng:
Voltage DC Open Loop Value Range Unite Reading Uint 100 mV OL mV 1 V 0.128 V 10 V 0.128 V 100 V 4.08 V 1000 V 3.95 V Current DC Open Loop Value Range Unite Reading Uint 100 µA OL µA 1 mA 0.41 mA 10 mA OL mA 100 mA 41.5 mA 400 mA 41.5 mA 1 A OL A 3 A OL A 10 A 4.22 A Resistance Short Loop Value Range Unite Reading Uint 10 Ω 8.08 Ω 100 Ω 40.73 Ω 1 KΩ 0.0406 KΩ 10 KΩ 0.0406 KΩ 100 KΩ 4.04 KΩ 1 MΩ 0.0039 MΩ 10 MΩ 0.039 MΩ 100 MΩ 0.039 MΩ 1 GΩ 0.039 GΩ The Reaging of the applied value on the range adds to half the applied value + the readings in the above tabels For Example at range 10 ohm the value show up 8.08 if we applied 1 ohm it will equal (8.08 + (applied Value /2)) and it shows 8.58 ohm For Example at range 100 ohm the value show up 40.73 if we applied 100 ohm it will equal (40.73 + (applied Value /2)) and it shows 90.73 ohm For Example at range 100mA the value show up 41.5 if we applied 10 mA it will equal (41.5 + (applied Value /2)) and it shows 46.5 mA Voltage AC Open Loop Value Range Unite Reading Uint 100 mV 7.3 mV 1 V 0.0072 V 10 V 0.0072 V 100 V 0.0475 V 1000 V 0.638 V Current AC Open Loop Value Range Unite Reading Uint 100 µA 0.09 µA 1 mA 0.0006 mA 10 mA 0.005 mA 100 mA 0.06 mA 400 mA 0.575 mA 1 A 0.00087 A 3 A 0.0057 A 10 A 0.0062 A |
| MathWizard:
Voltage and Ohms often share some of the same resistors in their divider networks. But they don't usually share divider resistors with the current sensing. All 3 might also share some of the same connecting switches, either electronic switches, or mechanical. I've only worked on a few DMM's, but yeah I wonder what's wrong with the current measurement, and if it's related to the others ? Usually, the amp signal into the DMM, takes a different path right away, than a voltage signal. But then their sampled signal, might go through the same analog switch IC's. If only the ADC section had a problem, I'd expect errors on AC too. I'd trace the path of the V/R into the DMM, and check their divider networks and switches, and then see where Amp signals go. Here's a link to some manuals, but I don't see a service manual, maybe it's too new a DMM by the late 90's ? https://www.manualslib.com/products/Fluke-8846a-2791364.html |
| coromonadalix:
8845 8846 meters schematics never leaked, and i'm not aware of any reverse ... only heard about dim display, and many network related problems |
| Kleinstein:
As the AC part seem to work somewhat this suggests that the ADC part could still work and the problem is more with the input amplifier or signal switching at the input. The ohms part usually is a combination of a switchable current source and a voltage reading. So the gain from the voltage part is usually shared. The current source is usually separate. However in some of the better meter Fluke also has a somewhat non stanard way to implement the ohms modes. The current part would have shunts and than usually use the lowest DC range, in some cases the 1 V range. A simple point one could test is the test current from the ohms source. So measure the current with an external meter when in the ohms ranges. The may give a clue if the factor 0.5 comes from there. Another simple point is checking if there is significant input current when in voltage mode. |
| coromonadalix:
don't double post .... in the beginner thread |
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