I recently bought for less than 150 USD, a rare second-hand Fluke 185 DMM, which was first released in 2000, as part of the 180 family, which included the 187 and 189. The lesser Fluke 183 was also available, but came without temperature and 4~20mA loop measurement and with less memory and accuracy. In those days, the 185 wasn’t cheap, selling for about 450 USD in the UK. As you can see, the meter I bought on eBay is in pristine condition.
The meters had originally been developed and produced by Tektronix as the TX3 and TX1 multimeters.
It isn’t clear, to me at least, why Fluke decided to include Tektronix meters in their line-up. Strangely, some old Fluke ads I found, mentioned that the meters were only available in the European market.
The Fluke 185 was sold with a set of TL75 leads, alligator clips and a user manual. It was identical to the Tektronix model, apart from a different rubber boot and an 11A rated fuse instead of 15A on the TX3.
Mine was sold without the test leads and also without the bail, which went AWOL a long time ago. I think that the original meter came with a small rubber insert to secure the serial cable to the top of the meter. That’s also gone missing.
While I have your attention, if anyone knows of 185 spare parts anywhere, I would be keen to acquire the ones missing on my meter, especially the original bail.
1. Ergonomics:The meter is unusual, as some of the range selections are made through the top F1 to F4 keys, with the relevant labels appearing on the large LCD screen. It also has a single jack for current measurement and a single position on the range switch, while retaining the usual uA, mA and A ranges. The automatic or manual switching between the current ranges (10A~500uA) is seamless, with no interruption of the circuit under test, as happens with conventional multimeters.
I found the 7 position range switch a little stiff, but the strong spring action makes intermediate positions near impossible.
Although the meter comes with a good protective rubber boot, the large LCD screen will most likely get damaged in a fall, if it comes in contact with a sharp object.
The bail has an extra position, where it tilts to 90 degrees, allowing a sliding rubber insert to provide a secure grip on a ledge, for hands-free measurements. Normal bail position reclines the meter to a 45 degree angle.
The cover for the 2 AA batteries unclips very easily, making battery replacement in the field, a cinch.
It is not a small or light meter at 200x100x50 mm and 540gr with the holster on.
2. Features:The true RMS (AC+DC) meter comes with the usual DMM features, plus 4-20mA process loop measurements with % readout, dB/dBm, Auto Hold, Min-Max, Peak Hold and enough memory for 30 readings with time stamps. Values can be recalled and read on the screen.
Two IR LEDs are used for serial PC logging and calibration.
The continuity test is lightning fast and latched (<1ms, 1.25V open voltage and 250uA). Why can’t all meters be like that?
For frequency measurement, the Fluke 185 is always AC coupled, unless the duty cycle mode (+ or - option) is activated. It then becomes DC coupled on all relevant ranges. Like the Fluke 87V, triggering can be changed from rising to falling edge, which may help with an unstable waveform.
Remaining battery voltage can be displayed and warning messages appear for a ruptured fuse or test lead placement when the selector leaves the amp range.
Soft green LEDs light up the screen on request with an adjustable timer to save batteries. The timer can be disabled, providing continuous lighting, when necessary.
A K-type probe is required for temperature measurement, with the possibility of ice bath calibration for better accuracy, with the offset amount retained in memory. Ambient temperature is displayed in the secondary window at the same time as probe temperature.
The meter, like the Fluke 289, has an unusual 50 Ohm range, where it prompts the user to short the test leads for automatic zeroing and then increases the test open voltage to 1.2V instead of 300mV, presumably for better accuracy.
I couldn't see much difference in accuracy between the two resistance measuring modes.
Measuring a resistor of 5.615 Ohms (4W value), gave me fluctuations between 5.58 and 5.62 Ohms in both modes, giving the meter 5 minutes to settle down.
Some screenshots of the Min/Max and Fast Min/Max in operation for a 4Vpp sine wave:
Max, Min and Avg show the RMS value of 1.414V. Max-Min shows the small difference between Max and Min. (1-4 samples per second)
Fast Max shows the upper limit of the sine wave (2V), Fast Min shows the lower limit of the sine wave (-2V) and Max-Min shows the Vpp value of 4V (1 sample per mS). That information also allows you to calculate the crest factor (Vpp/RMS) to see if your measurement is within the meter's accuracy statement (Max crest factor 3~6).
The diode test is pretty useful, the meter being able to light up white (80uA), green (210uA), yellow (210uA) and red (210uA) LEDs and also display the voltage drop for each of them. I haven't tried a blue LED yet. Open voltage is 3.3V. Standard diode like 1N4002 has a test current of 480uA.
3. Safety:The meter is rated for CAT III/1000V CAT IV/600V with the usual Fluke safety standards and independent testing. The protection consists of 1 PTC, 2 spark gaps, 1 fusible resistor and one 11 amp 1000V HRC fuse, catering for all ranges.
4. Accuracy:The meter can be set up to be used with a fast 5,000 count or a slower 50,000 high resolution mode, with a DC accuracy of 0.05%+1 (+10 in HiRes mode). The last closed-case calibration date is retained in memory.
My meter was never calibrated and has the original software version. After some comparison tests, I have established that for the most part, it has remained within the published one-year tolerance.
True RMS bandwidth is a respectable 20kHz for voltage and 5kHz for current, with a crest factor between 3 and 6.
Capacitance resolution is 1pF and the highest range is 50mF. A 5mF capacitor takes about 8 seconds for a reading (5,000 count only).
Calibration manual:
http://www.transmille.net/ProCal/Procedure%20Library/Fluke%20Digital%20Multimeter%20185%20%5b1.10%5d/Technical%20Data/Fluke%20183-185%20(PN%201610436%20Rev%201%206-02)%20Calibration%20Manual.pdf5. Construction:Two self-tapper screws hold the two halves of the meter together, with the help of two locking tabs at the top of the meter.
The batteries are held in a separate compartment which clips on the main body of the meter.
The double-sided PCB is held in place by 2 self-tapper screws in the middle of the board and a few clips at the top.
The circuit design doesn’t need a mA fuse, as any overcurrent is automatically routed to the beefiest MOSFETs and the 11A fuse. My board has the Fluke reference on the silkscreen, including the revision number 003, with 007 hand-written underneath it.
Less elegant are the 3V battery leads snaking haphazardly to the 3V and 5V DC to DC converters, on the top half of the PCB.
The band-gap voltage reference is a 1.2V Maxim ICL8069BCSA with 1ppm/1000hr long term stability and a max tempco of 25ppm/C.
Strangely, a loose pogo stick is used to make contact with the shielding plate in the bottom half of the meter case.
The major PCB components are:
3 microcontrollers
2 power MOSFETs IR L2203NS (HEXFET)
2 PhotoMOS relays
3 Dale Vishay current shunts (50, 0.5 and 0,005 Ohms)
1 NAiS relay
1 EEPROM
2 crystal oscillators
DC to DC converters for 3V and 5V
2 IR diodes
1 Maxim band-gap voltage reference 1.2V ICL8069BCSA (1ppm/1000hr 25ppm/C)
6. Operation:I like the logical layout of the function keys, which makes the meter very user-friendly, especially if it is used infrequently.
One only has to remember to push the yellow button for 2 seconds, to access the menu and most of the available settings.
Unusually, the burden voltage is very low on the 500 uA range, as the current shunt is a meager 50 Ohms (50uV/uA on the 500uA scale, equal to half the burden voltage of the Fluke 87V or Fluke 189, which is pretty good already) .
The ‘Auto Hold’ takes a reading with a beep after approximately 1 second of probe contact.
The bar graph has 20 segments with 20 updates per second.
The small 30 readings memory size seems weird by today’s standards, but still useful if one doesn’t have the dedicated serial PC logging cable. Data can only be saved manually in memory, by pressing the STO key repeatedly. The meter is compatible with the FlukeView Forms software (version 1.6 or higher). Both software and special cable are still available from Fluke (FVF-SC2).
Fluke 185 manual:
https://www.eevblog.com/forum/testgear/fluke-185-review/?action=dlattach;attach=127443
Keep in mind that the update speed is slow in HiRes mode, at one update per second, instead of four. Also remember to discharge caps before measurement to avoid any damage.
The screen green lighting is average at best, but does the job and what I like the most is that it can be kept on at will for lengthy measurements in dark places.
Here are screen shots of the AC, AC+DC, dB and dBm displays for a test 2Vpp sine wave with a 1V offset, to highlight easiness of operation.
True RMS AC is 0.707V
True RMS AC+DC is 1.22V (SQRT(0.707^2+1^2))
-3dB [20 log V/Vref(1V)]
-0.79dBm [10 log 10^3 x V^2/Rref (Rref=600Ohm audio standard and 1mW reference)]
The dB 1V reference can be modified in the menu and the new value retained until the meter is switched off.
Frequency measurement is good up to 1MHz. Duty cycle can be toggled between positive or negative percentage in the menu and is displayed at the same time as the frequency on the screen. The meter also gives you a choice of triggering either on the upslope or downslope of the waveform.
7. Final Assessment:To conclude, I think that the most attractive features of this meter apart from the low price, are the fast continuity test, the continuous amp range, the low burden voltage and diode test current.
Features that let it down a little are the small memory size, the cumbersome access to the 11A fuse, the slow screen update rate in HiRes mode and the lack of a cap discharge circuit.
Still, it is my favorite meter at the moment, just for the simplicity of its user interface, the sophistication of measurements and the legendary USA made Fluke quality, even if the meter was conceived by Tektronix.
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