DMM BTMeter BT-570C-APP

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This is a DC clamp meter with common DMM functions and a Bluetooth interface and app.

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The box is for a lot of different meters and there is a comparison list on the back.

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Inside the box is a pouch with everything in it.

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The package included the DMM, a pair of probes, a thermocoupler and a manual in addition to the pouch.

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The probes are without any tip covers, this means the CAT III rating is wrong.

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The plug is shrouded.

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The thermocoupler is designed for insertion into stuff and is with a banana plugs-

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Display

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All the segments on the display.

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Typical display during usage with the range and the value. The RS232 is always on and is used for Bluetooth connection.



Functions

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Buttons: Rotary switch:

Input

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The clamp is for current measurements, it can go around 45mm, but it will touch.

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Measurements 1uF

A look at the capacitance measurement waveform.

DMMInputVoltageSweepHz

Frequency input resistance depends on input voltage.

DMMInputVoltageSweepmVDC

The mVDC range is high impedance, until the protection clamps.

DMMschema

200A range will show values up to 400A
Even with REL the 50nF range is 0.3nF out.



Android application

The application must be downloaded from a Chinese website and installed locally.

1s

The startup picture for the application, to start just press Start, I did not have to do any matching for it to work.

2s 10s 9s

After pressing start it will show a analog value using either a 40 or a 100 scale and the digital value with captured min and max values.
Going out of Bluetooth range and into range again lost some data, but not the connection.

7s 8s 3s

Sweeping sideways or using the buttons at the bottom it is possible to get a table or curve. The table can be saved in text format, Excel did not work.

6s 4s 5s

The option page allows adjustment of the sample rate and there is a about page.

logFormat

The saved text format uses date-time as filename, this means it is possible to save many logs. The format is plain text with spaces between elements.



Tear down

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3 screws and the meter was open

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I had a little problem taking out the circuit board, the clamp must be removed first. I first discovered that after removing all the 5 screws in the circuit board and 2 in the Bluetooth module. The clamp was 3 screws.

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The clamp is two sealed parts with the sensors in one part.

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For the clamp input is a OpAmp (IC4: TL052C Dual low offset OpAmp), with two voltage regulators (IC2 & IC3: 75301: 3.0V) nearby, probably one for the OpAmp and one for the rest of the meter.
The input terminal goes directly to a PTC followed by the input resistors (R28 & R29: 2x5Mohm), but the PTC is bypassed for the another resistor (R33: 900kOhm) and just after the PTC there is a track directly to the range switch. In ohm the input through the PTC is connected to a clamp transistor (T5) at the range selection resistors. The frequency and temperature input use the PTC, a capacitor parallel with a resistor (C8 & R21: 100kOhms) and then to the chip.
There is a few diodes (Q1, Q2, Q3) for range switch encoding. The main chip (IC1: FS9721-LP3) is a 4000 count multimeter chip.

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On this side is the pads for the LCD, the rotary switch and the buttons, but there is also some trim pots? How is they adjusted?

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A closer inspection of the enclosure showed how, there is a cover that can be removed.

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The Bluetooth module is a small Bluetooth module on a circuit board, it uses a Dialog DA14580 chip.

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Conclusion

As usual the protection is not up to a CAT III rating, it will probably work at mains voltage, but transients will kill the meter.
The meter works, a minor detail is bad calibration on the low capacity range, a more serious problem is that the meter will show wrong values due to low battery, before it reports a low battery.
The Bluetooth was easy to get working, but the export format could be better.
With the high current ranges the meter is mostly for high power applications and the safety is not good enough for that!



Notes

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