DMM Peakmeter MS8229

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This is a cheap DMM with all common function and some environment functions.

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It arrived in a generic DMM box with no information on it.

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It included the DMM, a pair of probes, a thermocoupler, batteries, a bag and a manual.

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The probes has removable tip covers. The CAT rating is marked on the tip and will change when the cover is removed.

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The plug is fully shrouded and a bit shorter than standard size.

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The meter includes a cheap thermocoupler.

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The tilting bale is stable enough to use the switch and buttons.
The range switch has very loud clicks, this can avoided by turning it carefully.

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The environment sensors.

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Display

The meter do not show all segments during power on.

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Typical display during usage, it will show the number and what measurement is selected.
The display will always show humidity and ambient temperature, but they need a few second to initialize when powering on.



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.

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There is a 5 offset with thermocoupler when it is at zero.



Tear down

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Four screws and the back could be removed.

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The circuit board is shaped to use the box fairly well. There is four screws holding the circuit board and 3 screws holding the display.

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The sensors on the front uses two cables, one for lux, temperature and humidity and another for sound.

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The top of the meter with holes for the sensors.

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All four sensors, a photo diode, a humidity sensitive resistor, a temperature sensitive resistors and a microphone.

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On this side of the circuit board is the switches and the lcd display.

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There is nothing under the lcd display, except the backlight module.

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The white block is the backlight module, the pink part is the zebra stribe that connects the display to the circuit board.

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R63 is the 99ohm uA shunt and R66 is the 0.99ohm mA shunt, the chip near the resistors (VR1: 7530-1) is a 3 volt regulator. The 10A shunt is the wire at the bottom. The fuses are rated for 1000V and are the long type. But I am missing protection for the current sense resistor, this will usual be a couple of diodes.
At the voltage input is two PTC's one going to a 10Mohm input (R37+R38: 2x5Mohm) and on going to a 150Mohm input (R80, R81, R82: 3x47M). The transistors Q7 and Q9 looks like input protection. There is no MOV's to limit the voltage to the range switch.
The meter has two main chips: U7 is the DMM frontend and U2 is the processor, U1 is probably a EEPROM, the 3 trimpots on the circuit board is not enough to trim all the ranges. The handling of the environment sensors are U4, U5 and U6, all placed where the wires from the sensors are connected.

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Conclusion

As usual I doubt the CAT rating, this meter do have some protection, but not enough. The environment sensors can be used, but sound is very bad and light is probably about the same as a cheap lux meter, except it only has two ranges.
The DMM functions are fairly standard, as usual the high mA range has a high burden voltage.



Notes

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