Digital Multimeters (DMM)

Brooke Clarke 2010 - 2015

Background
Probes 
Accessories
Patents
Gardner Bender GDT-3200
Related
Links
Fig 1 Fluke 87V Box
Fluke 88
                Digital Multimeter (DMM) Box
Fig 2 Fluke 87V Included in Box
Fluke 88
                Digital Multimeter (DMM) Included
Fig 3 Fluke 87V Front
Fluke 87V
                Front
Fig 4 Fluke 87 Front
Fluke 87
                Front
Fig 5 Fluke 12 Front
Fluke 12
                Front
Fig 6 Fluke 87V Back
Fluke 87V
                Back
Fig 7 Fluke 87 Back
Fluke 87
                Back
Fig 8 Fluke 12 Back
Fluke 12
                Back

Background

Prior to using the Fluke Digital Multimteres I used the cheap ones, like from Radio Shack.  They say "to error is human" and when you error with a DMM  it's usually something like forgetting to change from Ohms to AC volts and then sticking the probes into the A.C. mains outlet.  The next thing is you get to watch and smell the smoke coming out of the meter.  Sometimes the destructive energy is not great enough to let the smoke out and you just get wrong readings.

The cure for that is to use the Fluke (or other high end) DMMs that are designed to withstand that kind of abuse. This is my second model 87. 

I wore out the switch on my first model 87 (I don't think they had the lifetime warranty then.) and sometimes it does not turn off and so drains the battery.

Over the years I've used many many multimeters.  One was in EICO kit ik Ohm/V analog meter and got me on San Fransisco channel 9 for building it.
Another was the Heathkit VTVM I still have, but the plastic analog meter bezel was broken.

There are times when one is a better choice than another.  When troubleshooting something like a lawn sprinkler system the Fluke 12 or a very cheap analog multimeter (1k Ohm/volt) works much better than the Fluke 87 or a VTVM because the cheap meter (or Fluke 12) presents a load when measuring voltage and so a break in the wire shows up.  But if you use the Fluke 87 (hi-Z input) you see the supply voltage because there's no load to pull it down.  The Fluke 12 has an internal resistor shunting the Voltage input in the VCheck mode for just this reason.

I haven't tried it but suspect that the Max/Min/Average function on a Fluke 87 DMM could be used on telephone dials to good effect.

I spent a few decades working with semiconductors and the Vf measurement, when done at 1.0 ma, is a very useful thing to know about a diode.  The Fluke 87 uses a 1.0 ma current source for the diode function, but other meters may simply use a resistor (not a current supply) and so the Vf value is not as useful.

Note by measuring a transistor with the diode function with both polarities (E-B, B-E, C-B, B-C) you should see two forward diodes and something approaching an open circuit on a good transistor that's not connected to anything else.  This can be used to identify which wire is which and tell if it's an NPN or PNP.   But there are transistor testers that do a much better job and some work while the transistor in installed in a circuit.

Another thing that's nice about the Fluke 87 is that he AC measurements are true RMS rather than displaying an RMS value based on using peak detection of the waveform.  The latter method works if the signal is a pure sinewave, but is in error for other waveforms.

I tried to measure the short current output (Flash Amps) of some No. 6  1.5 Volt batteries with the Fluke 87, but the current was so high it blew out the internal protection fuse.  Those fuses are pricey.  When No. 6 batteries were popular there were pocket analog current meters (not voltmeters) that were used to check the "flash amps".

Probes

I've had a problem with some probes that have opened.  This was caused by poor strain relief.  I'll see if I can find the dead ones to add a photo.

Good probes have sharp points which allows probing fine pitch Surface Mount Technology parts as well as probing through conformal coating.
Fluke and Greenley have nice sharp pointed probes.

Accessories

LCA-10 A.C. Line Current Test Adapter

Fluke
                    LCA-10 A.C. Line Current Test Adaptor

80i-400 A.C. Current Clamp

Fluke
                    80i-400 A.C. Current Clamp

80T-150U F/C 1 mv/deg Temp Probe

Fluke
                    80T-150U F/C 1 mv/deg Temp Probe

85 R.F. Probe

Fluke 85
                    RF Probe

Type K Thermocouple Temp Probe

Fluke
                    Type K Thermocouple


Fluke DMM Patents

4335349 Simulated ohms generation method and apparatus for calibrating resistance ...
4389708 Method and apparatus for enhancing the output of an RMS converter -
D280299 Digital multimeter for electrical measurement - 10 series?
D281864 Electronic instrument meter cover -
D282532 Multimeter
D337435 Multimeter holster
D446735 Digital multimeter
D295148 Digital multimeter accessory
4841229 Method of and circuit for ohmmeter calibration
4847507 Fiber optic guard crossing of circuits having analog and digital sections
4860289 Reset circuit for electrically isolated circuits communicating via uart
4864512 Measurement apparatus with plural displays of measured parameter and ...
4940204 Instrument having flexible stand
4947355 Modular electronic instrument system having automated calibration capability
5012181 Apparatus for and method of internally calibrating an electrical calibrator
D314715 Digital multimeter
5073757 Apparatus for and method of measuring capacitance of a capacitive element
5122627 Asymmetrical electrical switch actuator
5142221 Automatic function selecting multimeter
5146390 LCD support bracket
5218290 Multi-function, multi-mode switch for an instrument
5186634 Electrical contact having spring-biased tabs for mounting to a circuit board
5227984 Instrument with continuity capture feature
5379176 Protective input circuit for an instrument
5418450 Coupling circuit for a measuring instrument
5432706 Multimeter having min/max time stamp
D359006 Digital clamp meter
5508607 Electronic test instrument for component test
5512841 Peak current detection in a test instrument for ensuring validity of ...
D369306 Graphic multimeter instrument
5530373 Method and apparatus for determining and selectively displaying valid Measurement Information
5594329 Method and apparatus for obtaining voltage-isolated measurement channels ...
5691635 Probe identification system for a measurement instrument
5698984 Adaptive digital filter for improved measurement accuracy in an electronic ...
5705936 Method and apparatus for automatically testing semiconductor diodes
5839633 Multimeter belt holster
5920188 Voltage measurement instrument having transient overvoltage input protection
5930745 Front-end architecture for a measurement instrument
6043640 Multimeter with current sensor
6094045 Input ranging circuit for an electronic instrument, (Fluke), Jul 25, 2000, 324/158.1; 324/115; 324/731 -
6094949 Lock device for electronic test apparatus
6163445 Low-voltage test signal path protection circuit with extended bandwidth ...
6191723 Fast capacitance measurement
6201320 Automatic power turn-on circuit for a battery-powered voltage measurement ...
6275047 Capacitance measurement, (Fluke), Aug 14, 2001, 324/678; 324/548 -
6281673 Low error, switchable measurement lead detect circuit
6318687 Accessory mount
6392402 High crest factor rms measurement method
6466003 Microamp measurement for two-terminal digital meter
6469492 Precision RMS measurement
6624640 Capacitance measurement, (Fluke), Sep 23, 2003, 324/678; 324/658; 324/677 -
6628113 Surge current measurement
7242173 Combined test instrument probe and voltage detector
7342393 Multimeter with filtered measurement mode
D562317 Digital multimeter case

Gardner Bender GDT-3200 Multi-Meter

June 12, 2015 - Got this at the local hardware emporium to use while my Fluke 87 DMM is repaired.  There were a number of multimeters for less money, but they seemed cheap.  This one seemed more rugged.  While none where as solid as the Fluke, it's useable.

It has a battery test function which has a resistive load across the input DCV terminals.  This could also be used like the VCheck feature on some Fluke DMMs.
At 3.0 Volts it draws 43ma, at 10 Volts it draws 142 mA this is consistent with a 70 Ohm load resistance.
That's to say it has more uses than just checking batteries.

The strap has a (GB) logo that's also a magnet with enough strength to hold the meter and test leads on an iron or steel surface.

Fig 1 In blister pack
Gardner
                  Bender GDT-3200 Multi-Meter
Fig 2 Includes both normal test leads
and a (type-K?) thermocouple
Gardner
                  Bender GDT-3200 Multi-Meter
Fig 3 Uses a couple of triple A (AAA) batteries
Gardner
                  Bender GDT-3200 Multi-Meter
Fig 4  The gray "mode" button switches between:
Diode & Beeper
deg F & deg C
The black button (after 2 seconds down) turns on
 a back light
Gardner
                  Bender GDT-3200 Multi-Meter


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