DMM Southwire 16040T

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Southwire is an American wire and cable company and have a couple of DMM's in their range. This is a fairly compact meter with most of the common DMM functions and a few extra.

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The meter is sold in a clamshell box with comparison to other Southwire meters on the back.

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The box contains the meter, probes and a manual, it is also possible to download a manual.

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The probes are rated for 600V and 10A in CATIV environment, this is a very good rating.

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The removable tip must be on for best safety

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The standard size plug is fully shrouded.

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The tilting bale locks in both position (in and out). It might be possible to switch range on a non-slip surface, but it is difficult on a normal table.

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Both fuses and batteries can be replaces by removing a lid.

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The flashlight.

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The probes looks fairly large on this small 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 the meter.

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Typical display during usage, it will show the number and what measurement is selected.
The circle with arrow shows that auto power off is enabled, hold down MODE when turning on to disable this.



Functions

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Buttons:
Rotary switch:

Input

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Measurements

1uF

A look at the capacity measurement waveform, it is non-polarized.

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Application

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The application will show the meter reading and can record the values. It is also possible to control the meter (Only the buttons, not the range switch).
The curve on the screen is moving fairly fast and will only show the last few seconds.



Tear down

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I had to remove 4 screws to open it.

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The back contains a circuit board with the flashlight led and connections from the batteries.

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The circuit board is build to fit exactly into the DMM.

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There is two layers of circuit board, the top layer with fuses and the input connections.

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It was mounted with two screws and connectors for the signals.

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The two resistors (R80 & R81 99ohm & 1ohm) are the uA and mA shunts. At the connector is a mA, uA and a value connections, the value connections makes it possible to measure the voltage ignoring losses in the connector and switch.
The diodes (D2, D4, D7, D8 and Z2) are protection for the shunt resistors.

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Four more screws and the circuit board could be removed.

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And four more screws to removed the lcd display.

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On this side is a microprocessor (U1: MSP430F449 16bit, 60+256K flash and 2K ram) and a Bluetooth module.
The input voltage is connected to this circuit board via a screw and there are a couple of PTC's and a gas discharge arrestor

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On this side there are a few more gas discharge arrestors and a PTC more. There is also some transistors used for protection (Q4 &Q6, Q3 & Q5). There is a resistor chain with smd (R103, R104, R105, R106, R107: 15Mohm) and one with through hole resistors (R31 & R32: 10Mohm).
The square chip is the multimeter chip (U9: DTA0660L) with its EEPROM (U10: 24LC02).
It looks like a boost circuit near the buzzer: U16 is the controller and Q22 and D3 the switching parts, this must be the reason for the stable backlight and flashlight.

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Conclusion

This is a rather small meter, but fairly thick. It has the most common functions for a DMM, it is only missing temperature. It adds Bluetooth and a flashlight. The shared voltage/current terminal is necessary for this small size, but is an added risk for mistakes.
The safety looks to be good, but I wonder about the fairly small fuse size.
I like the Bluetooth, it makes it easy to read the display from a few meters distance, but I am missing some alligator clips with the supplied probes.
It is not rated for high precision, but it is fairly precise, with exception of the low capacity range everything was only a few counts out.

This is a good meter both for mains related stuff and for hobby, it is easy to put into a pocket or toolbag, but I would keep it away from really high current stuff.



Notes

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