DMM Amprobe AM-570

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This is the top meter in the Amprobe 5xx series, it is well packed with functions and has fairly good specifications.

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The meter is packed in a clamshell box, on the front it has some highlights for this meter and on the back it compares the different models in the 5xx series.
The 540 and 550 is missing, they are basically the same as 560 and 570, but with different safety ratings and only sold in EU.

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It included the DMM, a pouch, a pair of probes, two thermocouples and a dual thermocoupler adapter, a safety information sheet and a mini CD with the manual (It can also be downloaded).

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I forgot this strap in the above picture. It can be used to hang the meter from all types of hooks.

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Everything could fit in the supplied pouch.

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The two thermocouplers are standard K type with a standard K type plug.

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The thermocoupler adapter takes two standard thermocouplers and connect them to 3 terminals on the meter. T1 is volt input and common, T2 is mAuA input and common, in both cases common is the negative terminal.
This also means it is possible to use one thermocoupler with banana plugs as either T1 or T2.

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Probes are branded with Amprobe and has removeable tip covers.

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The plug is fully shrouded and standard probe plug size.

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The meter has a led at the front for flashlight usage, it is behind a plastic window.

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The tilting bale works very well, it is easy to extended and the rubber feet secures the meter do not slide around when pushing buttons or turning the range switch.

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Display

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The above picture shows all the segments on the display.

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Typical display during usage, it will show the main number and what measurement is selected. In addition to this a secondary readout with frequency will be shows in AC modes, with max or min in max/min mode and with base value for REL modes. It is not used for dual thermocouplers.

NCV do not have its down display, it shows OL on the display and only indication of mains is the buzzer.



Functions

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Buttons: Rotary switch:
Input

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The thermocoupler adapter with two thermocouplers.


Measurements 1uF

A look at the capacity measurement waveform.

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Frequency input resistance.

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Actual burden voltage at 6mA is 0.96 volt an internal diode bridge reduces the burden voltage at higher currents.
Actual burden voltage at 600mA is 2.05 volt an internal diode bridge reduces the burden voltage at higher currents.
With high DC voltage present the AC range will not show low AC voltages.
NCV only use buzzer as indication, not light or display.


Tear down

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3 screws (One was for the battery cover) and the back could be removed.

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The circuit board is shaped to follow the shape of the box. In addition to the screws there are two clips at to keep the circuit board in place.

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Four screws and I could take the circuit board out, the input terminals was rather difficult to get out.
Only the two screws was necessary, the two at the top was only for the display cover.

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There is some shielding in the plastic for the ampere input. It matches slots in the circuit board.

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There is some electronic below the display.

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There protection for R80 in the current shunt (D10, D11, D15, D16) is on this side. The 10A sense line has a series resistor (R25 5Mohm). The 400kohm switch is 4 switches and two resistors (R53, R54, 2x200K) in series.
There is two leds for background light to the LCD display.
The big chips is a microprocessor (MSP430F5310 with 32K program memory and 6K ram) and there is a EEPROM (IC5: ATMLH838).

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There is a lot of input protection on this meter. Two sets of double PTC's (PTC1, PTC2, PTC3, PTC5) followed by dual MOV's (SG1, SG1, SG3, SG4) and then lots of transistors pairs, some of them with fairly large transistors (Q7, Q8 & Q9, Q10 & Q11, Q12 & Q13, Q14 & Q16, Q17). The MOV (SG5) besides the 0.5A fuse is probable protection for T2 input). The 10Mohm input is made from four resistors (R1, R2, R3, R4: 4x2.5Mohm).
The full current shunt protection (D3, D4, D5, D6, D9) is missing
The actual current shunt is a bit special, it uses a couple of resistors in series and parallel (R33, R34: 2x1ohm in parallel, R80, R32, R81: 4.5ohm, 45ohm, 450ohm in series). This makes the mA current shunt 0.5ohm + 4.5ohm with diodes and explains the very bad burden voltage. In the uA shunt the diodes clamps the 450ohm resistor.
The two large chips are a DMM frontend (IC2: ES51995A: 6000 count) and a LCD driver (IC1: BU9799KV). The frontend has an external True RMS converter (IC6: ES636: 200 segment driver). There is also a charge pump (IC4: CAT550) making a negative voltage from the internal 3.5V that is made with a linear regulator (Q1).
At the top of the circuit board is the NCV antenna

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Conclusion

This is a fairly advanced meter with many functions and most of the working perfectly, but I do not like the uA and mA ranges, the burden voltage is way to high and I do not have confidence in the protection, because the diodes are missing (This circuit is from the DMM chip datasheet, there is also a circuit that requires an OpAmp and gives low burden voltage), the meter is also missing the low A range. The NCV is audio only, this is not a good solution.
Except for the above the meter is fairly good with lots of extra functions like: flashlight, Peak, LPF, dual temperature inputs, Low-Z.



Notes

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