| Products > Test Equipment |
| Hantek CC-65 AC/DC Current Probe Teardown and Testing |
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| RodgerTheBadger:
John, Many thanks, that makes sense now. I suspect two variable resistors are used to try and keep the temp co. the same on each side? If fixed resistors were used on one side and a trim on the other they would probably have different temperature coefficients, leading to inbalance with temperature change. Or maybe it is just to keep the parts list down to make assembly cheaper. Anyway, thank you for your reply :) Rodger |
| dcac:
--- Quote from: CDaniel on July 23, 2020, 12:56:28 pm ---Not very sure how the pot could work without some modifications , since the circuit is made to zero the output with no input , that's why is momentarily connected . With the button pressed you can't measure , it is just showing zero , when released and the wire removed from clamp it will show that last current value as the new zero level . If you don't want that function just remove R23 and use REL all the time . --- End quote --- Keep in mind you can only use REL as long as the offset is not too high. i.e. if you have a 50000 count meter and want to measure in the 50mV range - but you have 20mV offset canceled out with REL - you can then only measure up to 30mV before you get out of range. |
| Elasia:
Hmmm I've had one of these in a drawer for some years now... maybe i'll mod it... thing drifts so much its useless really less i want an instant measurement and only that one instant measurement.. |
| Elasia:
I slapped a 10uF chip cap right on the output to make it semi usable and cut the fuzz down It still drifts to no end making it utterly useless for time based tests less that charge cap is modded out |
| jrf:
Most of the time when I switch mine on at normal room temperature it is with in +/-1mV of Zero volts. (especially after tweaking VR3). Hence no point using zero button. The button should never be used for timed tests. This unit is not designed for 'measurements' below 50mA. It gives an indication below 50mA but not something I would trust, given the noise threshold of +/-10-15mA. Drift is caused by temperature change, using the Zero PB, or physically moving the clamp. So eliminating those issues will reduce drift to within +/-1mV. Given that most long term measurements involve measuring the change then initial zero is not critical. Adding an output filter for slow measurements to reduce the +/-10-15ma noise is also fine. Remember this unit is not a precision instrument. It is a cheep automotive clamp mostly used to measure currents above 100mA or to show the relative timing of switching events. ie injectors ect... Precision instrument amplifiers, circuitry & design layout COST & are hard to duplicate when the clamp heads core is included. This serves the purpose for which is was designed very well & is the cheapest reasonable option I have found. Pico sell a unit, with what I believe is basically the same circuit, for 2-3 times the cost & one can spend 5x the cost on other units for no gain. At about 10x the cost some units start to out perform it, but one needs to pay at least $700US to get a unit that may be designed to minimise the noise & achieve good accuracy, sensitivity & frequency response. These units will usually have two separate but complimentary measuring systems for the DC & AC components. One gets what one pays for has never been truer! Cheers, John. |
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