I recently purchased a digital multimeter from Maplin which was on sales at that time: Precision Gold N56FU. Being a full sized autoranging multimeter with computer interface, this meter £44.99 seems to worth every penny. Of course, Maplin didn’t make this meter. Some Chinese dudes did. Maplin just rebranded the meter because E-SUN sounded too lame =P
No purchase is complete until it is disassembled!
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Nope, certainly no FLUKE board, but still, it looks very solid.
1. The controller: FS9922-DMM4 from Fortune Semiconductor Ltd. You got to love those Taiwanese. They slapped two analogue to digital converters, voltage regulators, AC rectifier, LCD driver, RS232 driver, etc etc…onto a silicon slab. That’s basically EVERYTHING you need to create a modern digital multimeter on a single chip!
2. Infrared LED: If you’re wondering why there’s an infrared LED on the meter, trust me, you’re not alone. I was puzzled as well. Note: I removed the complimenting infrared receiver module for clarity reasons.
3. True RMS converter: AD737J from Analog Devices, which a quoted accuracy of ±0.2 mV. Sweet!
4. 640 mA fuse: To protect the micro/miliampere line.
5. 20 A fuse: To protect the 20A line.
6. Copper jumper: Well, if you want to pass 12 kW of juice through this meter, the bigger this copper jumper, the better.
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Look at the huge fuses!
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True RMS converter
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Infrared receiving unit. Notice the Silicon Labs CP2101 USB-to-UART converter chip (2). The IR receiver is located at (1) and the USB port at (3).
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If you were still wondering why on earth did E-SUN used infrareds instead of just hard wiring the the USB-to-UART chip to the controller, consider this: You are conducting a high voltage experiment. Due to budget cuts, your department crossed out FLUKE and gave you an N56FU instead. You hooked the meter up to the 415 V rig and connected it via USB to a £1500 notebook. You took the notebook and went behind the plexiglass shielding for protection.Your computer started charting impressive graphs of the equipment you were working on when suddenly, there was a flash a light and you get thrown ten feet away. Your meter was fried and so was your notebook. The plexiglass shield was still intact though….So what happened? Some incompetent lads wired your rig wrongly! A gazillion volts rained down your meter due to a premature capacitor discharge. The current travelled through the multimeter, through the USB cable, over the plexiglass, straight to your computer! Whao….busted!
Back to business! This is what we call Optical Isolation. The circuitry on the mainboard (1) converts RS232 to IrDA signals and beams it to a receiving unit (2) housed in tough, clear polycarbonate. The IrDA signals are then decoded and converted to a USB language that your computer understands. Note that there aren’t ANY electrical contact points between the mainboard and receiving unit. The circuitry on the receiver draws current from your USB port only, since high voltage electricity can still arc and jump into this circuitry if it isn’t 100% isolated. This way, you and your computer can remain safe (while the meter literally takes all the bashing).
Owing to the fact that this meter can do MORE things than a £150 FLUKE 116, and that SAFETY has been heavily emphasized, I would say this is the most value for money digital multimeter EVER.