Digital Multimeters (DMM)

Brooke Clarke 2010 - 2024

    Fluke TL175 Electrician's CAT rated
Test Leads
Gardner Bender GDT-3200
Measuring Inductance using Capacitance Range
DT-832 Digital Multimeter
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
Fig 4 Fluke 87 Front
Fluke 87
Fig 5 Fluke 12 Front
Fluke 12
Fig 6 Fluke 87V Back
Fluke 87V
Fig 7 Fluke 87 Back
Fluke 87
Fig 8 Fluke 12 Back
Fluke 12


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.

Some decades ago I heard a rumor that the Fluke 87 could be put into Ohms mode and the probes inserted into a 120 VAC wall socket.  While emailing Fluke about meters for finding the breaker associated with a dead outlet, aka Electrical Testers, I asked about this and the answer is:
"Yes the Fluke-87 can be in the ohms mode and be subjected to voltage up to 1000V without damaging the meter."

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  One was  EICO kit 1k 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 has 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".


I've had a problem with some probes that have opened (see Hints & Tips: Fluke Test Leads).  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.

Fluke TL175

These are intended for use with Electrical Testers where CAT ratings are important.
Maybe these will not have the wire failures of prior test leads?

Fuke TL175
                      Test Leads showing CAT II and CAT III positions
Top probe set to CAT II 1000V
Bottom probe set to CAT III 1000V, CAT IV 600 V

marked US Pats: 7880487, 8154316 - twist tip to extend/retract shroud.


LCA-10 A.C. Line Current Test Adapter

Use DMM in AC AMPs mode. 1:1.  Just inserts meter in series with hot wire.

                    LCA-10 A.C. Line Current Test Adaptor

80i-400 A.C. Current Clamp

                    80i-400 A.C. Current Clamp

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

Uses 9V battery.  When "Off" output is about 150 mV with fresh battery and <100mV with battery that needs to be replaced. Uses IC sensor so range limited to -50 to 150 C.
switch selects Off or 1mV/degF or 1mV/degC.
                    80T-150U F/C 1 mv/deg Temp Probe

85RF High Frequency Probe

0.1 to 200 MHz, 0.25 to 30 Vrms

Fluke 85
                    RF Probe

80BK-A Type K Thermocouple Temp Probe

-40 to 260C
The model 87V includes direct reading of Type-K probes.
 Fluke Type K Thermocouple

80T-IR Infrared Temperature Probe

0 to 500 Deg F Printed on unit [32 - 1000 deg F in manual] (1mV/deg F)  uses 9V battery.
Sort of works.  Reading depends on Emissivity (Wiki) of heat source, so can be off.
If the Type K thermocouple can be used, it's a far superior option.
Fluke 80T-IR
                      Infrared Temperature Probe

Test Leads

I have had problems with test leads breaking.  See Hints & Tips Fluke Test Leads.

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
7880487 Test lead probe with retractable insulative sleeve, Steven Charles Petrick, Fluke, 2011-02-01, - the shield can be extended (CAT III) or retracted (CAT II). TwistGuard TL-175
8154316 Method and apparatus for indexing an adjustable test probe tip, Chris W. Lagerberg, Roger Stark, Fluke, 2012-04-10, - TwistGuard TL-175

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 usable.  Note has CAT III rating on meter as do the test leads (maybe a mistake).  This is an Electrical Tester.

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.

Feb 2020 - threw it into trash.  Duracell AAA batteries corroded on negative end that also corroded the battery spring.
Also the Temperature probe no longer worked, showed OPEN on Fluke meter.
Still have the test leads.

Fig 1 In blister pack
                  Bender GDT-3200 Multi-Meter
Fig 2 Includes both normal test leads
and a (type-K?) thermocouple
                  Bender GDT-3200 Multi-Meter
Fig 3 Uses a couple of triple A (AAA) batteries
                  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
                  Bender GDT-3200 Multi-Meter

Measuring Inductance using Capacitance Range

YouTube: EEVblog 1465 - Your Multimeter Can Measure Inductors - Measure the inductor on a Capacitance range, then invert the capacitance display to get inductance.
Tried on the Fluke 87V with a 4.7 mH inductor and got no reading stepping through all the manual ranges.

DT-832 Digital Multimeter

This is one of the cheapest DMMs on the market.  Under $10 on eBay including shipping and maybe under $5 on Aliexpress.
The micro grabber test leads were about twice the price of the DT-832.
I got it to lean what the Test Signal function does because of this YouTube:
How to make Metal Detector using Multimeter, 3:23 - But nowhere on line is there an explanation what the DT-832 (or other digital multimeters with the signal out function) displays in the test signal mode.  They all say the display is "1".  But that's not the case.

Coil: 0.3mm (0.0118": 29AWG) wire wound on 90mm (3.5") form, 30 Turns.
20 pF cap connected in parallel with coil.  On line calculator 151 uH
Resonant frequency = 2.896 MHz
This metal locator is very similar to the Metal Detector based on the Joule Thief circuit.

The Test signal measures 1.695 VAC @ 60.54 Hz open circuit and the DT-832 displays 1.  When connected to a color changing LED it measures 1.406 VAC @ 60.48 Hz and the DT-832 displays -760

Here's another YouTube with the same idea:
metal detector kaise banaye||metal detector machine||metal detector app, gold detector app, 7:09 - Used the coil in an old loudspeaker which has 6 turns wrapped around the magnet (maybe the original coil is open), 1N4007 diode with the band pointing to the speaker.  Connect power cord green to coil and white to diode cathode.  Red meter wire to white (diode) and Black meter wire to green (coil).  If done correctly the meter will beep when in Test Signal mode.  It's not clear what indication you get when there's metal under the coil.


Fig 1 Installing 9V battery
DT-832 Digital Multimeter
Fig 2 Test Leads and manual included
DT-832 Digital Multimeter
Fig 3 Test Signal Mode.
Positive to long LED lead,
Switching to "diode" mode turns on LED,
but not enough power to cause color changing.
DT-832 Digital Multimeter


Electrical Testers
Test Equipment


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page created 9 Feb 2010.