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The readings are a little better tonight, for some weird reason.
Qm 1551 is at 12.58 volts
El cheapo digital is at 12.51 volts (new battery)
Power supply in built (moving coil) 14.8
Kingdom (moving coil) just over 12 volts.
Optilux (moving coil) is at 12.2 volts
This is the link to the instruction manual for the oscilloscope: http://www.wakamatsu-net.com/biz/EGO_DSOManual.pdf. Its the only thing I can find, so far and it has a slightly different display.
Not so easy to understand! Would be better with the instrument in front of you while you are reading through the instructions. Odd that it doesn't have AC coupling. It would be difficult to get an accurate peak to peak reading if the waveform has a DC bias. It will just take some getting used to.Quote:
Originally Posted by mudnut
You would think that, but the display is slightly different and the designations aren't the same letters, in the right order or even colour.
I have made a set of test leads which make it simple to measure the tacho signal across the resistor which is inline between the coil and gauge. It is a 1-1.8 volt square wave but is very noisy, with spikes created by the current collapsing in the high voltage side of the coil.
The oscilloscope reads the AC signal from the speedo. It is just a matter or adjusting the Y offset to the centre of the grid. When connected to the 12 volt power supply, it also reads the pre-rectified signal as AC too, so I don't know why they reckon it is Only DC coupling. After working my way through all of the menus I have found measurements for V peak to peak, V rms, and V average, so forth.
I have also worked out how to set up the inbuilt Test Signal output. I can get it to closely resemble the Tacho signal, so I will try to get the tacho going too. With all the variables present in the circuits, I think a good frequency counter and function generator would be a good investment, If I decide to keep doing the clusters.
This is what I have found, so far in car and on the test bench. On the bench, I tried connecting a variable resistor grid across the tacho input and earth. With the Oscilloscope Test Signal 1.3 Volt square wave imposed across a 2.2 k resistor, but the tacho didn't move. I will have to get a function generator capable of producing a 9V bias. I might also have to tie the voltage to the 12v positive with another high value variable resistor.
I have found that the QM 1551 cannot read square wave duty cycles correctly. I will have to take it back and get another one sent out as getting the correct signal for a tacho will be essential to produce accurate readings.
The new multimeter turned up at the shop today. I took my meter in and hooked it, and the replacement up to oscilloscope test signal for the shop assistant. My meter was flickering up and down within in 3 to 5 Hz and the new one was steady as a rock. The shop assistant took the defective one and gave me the new meter, no worries. At home I have re-run some tests and am more impressed with the Jaycar QM1551. I thoroughly recommend it to anyone as an excellent and versatile tool.
R.I.P. the handheld oscilloscope, my bad.
I have been researching a replacement. I had a brain fart and bought an Allsun EM125 which is useless.
I am a bit averse to buying online, but I found this beast:
http://www.ebay.com/itm/HANTEK-Porta...-/290672129924
Has anyone dealt with Hantek equipment at all?
If you believe the specs the Hantek looks good, I have only just read this thread so I don't know what level of tech you are looking for.
I do know that Fluke multimeters give more stable & accurate measurements & they are reliable (still work after being dropped), they are what I would recommend to a customer, but are expensive for hobby use.
I am a bit spoilt when it comes to test equipment, 35 years in an avionics/instrument/calibration workshop.
Graham
I used to have Fluke meters at work, but the price is prohibitive for what I need. I was hoping someone had bought Hantek gear, and could tell me if the software was stable and reliable.