Hello,
I bought
this device for about $15 from company that handles products from customer returns from western Europe (mostly Germany, I think). It was advertised as "IR measurements are inaccurate". I thought that in worse case scenario with its nice narrow optics would still be an useful tool to quickly scan for temperature points that stand out even if absolute measurements were way out. In the best case it could be perfectly fine because customer who returned it wasn't familiar with concepts like emissivity. (I bought lots of perfectly working stuff from this company advertised as not working properly).
I received it today and indeed "measurements are innacurate". In fact the IR sensor seemed to not react whatsoever to whatever it was pointed at. Changing the the emissivity value does change the readout BUT it seems to be working the other way round. At E=1 display shows temperature of about 3degC, at E=0.5 its -32degC, at E=0.1 it goes lower than -60deg (offscale). I am pretty sure that is not the way it should work (with lower body emissivity higher positive correction should be applied).
Of course I immediately proceeded to teardown to see if there is any obvious fault. In the process of doing so I took some pictures I'd like to share with you
Here is how the boards are arranged internally (already took it out of the case and detached optics from IR sensor)
The whole thing consists of 4 boards. The sensor board (leftmost top), processor board (left), lcd/keypad board (right) and the board with K-type probe connector (bottom). Interestingly the bottom board seems to be also populated with some other sort of connector but it is neither connected to anything, not accessible in any way from the outside. Probably some form of production cost optimization by sharing parts with other products but still a bit strange.
Here is the different view of middle boards (populated side)
Model markings on the right board suggest that it may a relative to
DT-8856 infrared thermometer but I guess that only display board is reused since this one lacks USB/wireless connectivity option.
Some closeups of IC's on the main board.
HCF4053 - Triple 2-Channel Analog Multiplexer/Demultiplexer
Chipower CE7660- Charge Pump DC-DC Voltage Converter
NXP PCF8574T - Remote 8-bit I/O expander for I²C?bus with interrupt.
Microchip 24LC08B - 8K I2C Serial EEPROM
TI LSD4FE8232 - Obviously some sort of microcontroller. Couldn't find any datasheet but searching for this part number suggests that this is MSP430.
On the display board there is only one IC: PCF8576CT - unsurprisingly its Universal LCD driver for low multiplex rates
Other side of the boards:
Not much to see here.
On the main board there is a measurement button, buzzer, some configuration switches accessible from battery compartment and markings for JTAG and BSL connectors.
On the display board there are some marked jumpers. Maybe for triggering calibration or used during factory testing.
Last but not least: sensor board
Marking on the IC in the corner are unreadable at this angle but its AD8571 - Zero-Drift, Single-Supply, Rail-to-Rail Input/Output Operational Amplifier
Broken insulation on one of the sensor leads is a result of me checking its continuity.
The sensor itself:
I have problem finding any information on this one. I'll be glad if someone could shine some light on it.
Optics assembly feels very nice. Its body is cast from some alloy and it has proper infrared lens (germanium?) inside. Not a simple plastic fresnel found in cheaper units.
Interestingly after powering up the device without the optics assembly it started to react to some form of radiation. It alternates between previous state and overload when compact fluorescent light bulb enters the sensor field of view. Obviously lens must act also as a filter for everything except specific part of infrared spectrum.
I am pretty sure at this point that this device is beyond economical repair. Even if its something as simple as faulty opamp I doubt I could replace smd part by myself. Still, I'd like to investigate further on what could go wrong here. I am open for suggestions.