DMM PeakMeter PM18C

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PeakMeter has many fairly cheap meters in their program, this is manual range meter with a wide area of ranges (some of them with auto range).

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The box matches the meter, but there is no brand or model number on it, except a small sticker.

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It included the DMM, a pair of probes, a thermocoupler and a manual (No branding or model number in the manual, but it matches the meter).

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The probe are marked 20A and with the usual CAT ratings on the tip and tip cover.

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The shrouded plug is the short variety.

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The thermocoupler is the usual cheap model with two banana plugs.

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The range switch is a bit loud, but the clicks works very well for selecting the ranges.

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There is a flashlight on the back of the meter.

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Display

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The above picture shows all the segments on the display, not all are used by this meter.

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Typical display during usage, it will show the number and what measurement is selected.

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The NCV amd Live shows bar when nothing is detected

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And will show "NCV" or "LIVE" on the 7 segment display when something is detected. The actual strength is shown on the light bar and how fast the buzzer beeps.

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The light bar above the display if used in NCV, Live and Continuity. It may look like 6 segments, but it only has 3 leds!



Functions

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Buttons:
Rotary switch:

Input

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Measurements 1uF

A look at the capacitance measurement waveform.

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Frequency input resistance depends on input voltage.

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The meter cannot be used at 20A, the fuse did blow. At 10A the meter is 5% wrong.
The low capacitance range is 12% out.



The blown 20A fuse

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The fuse is marked 20A and with approvals.

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But I did not find any sand inside (Sand is used to prevent arcing when braking high voltage and current).



Tear down

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Four screws and the back could be removed.

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The flashlight led is mounted in the back (It cannot be removed without damage).

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The circuit board fits the enclosure and there is connectors for the battery and flashlight, but they are the same.

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There was 6 more screws to get the circuit board out.

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The backlight and LCD display was loose.

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At the voltage input are 3 paths: Voltage (r30 & R32: 2x5Mohm), drive for ohm and capacitance (PTC4 & PTC5), sense for these ranges (R8: 900kOhm). For the PTC there is a transistor pair for protection (Q1 & Q2). The uAmA current input has the usual clamping diodes (D1..D5) and 3 resistors (R14: 1ohm, R15: 9ohm (Not used as shunt) and R16: 1kOhm). The transistor tester has 4 resistors (R23, R24, R26: 20ohm, 100kohm, 2.7kohm), the last resistor in the row (R31: 10Mohm) is for the NCV antenna at the top.
The light bar above the display uses 3 leds with current limitig resistors (R28, R29, R35: 100ohm). The flashlight and backlight is controlled with a single transistor (Q3) and is powered directly from the battery with a series resistor (R65: 51ohm for flashlight, R18: 10ohm for backlight).
The voltage regulator for the meter (U3: 7530-1) is placed next to the power connector, the multimeter chip also has a EEEPROM (U2:24C02A) for calibration and functions.
It looks like the chip used is for autoranging meters, but here it is forced to do manual ranging.

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There is not much on this side, the 3 leds for the led bar, the socket for the transistor tester and the pads for the lcd and switches.

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Conclusion

The CAT rating is, as usual for cheap meters, wrong. A 250V fuse do not belong in a 1000V meter!
For a manual range meter this is fairly good, it has a lot of ranges, but not as many as a normal autoranging meter. The precision is good. The 20A range cannot do 20A only 10A and is not that precise.



Notes

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