| Products > Test Equipment |
| Hantek CC-65 AC/DC Current Probe Teardown and Testing |
| << < (20/33) > >> |
| dcac:
(lol) Well when I actually started looking at the caps values and the surrounding resistors it slowly hit me "100n" likely was just a 'place holder' for a sooner to be determined more accurate value. So after some searching I found my CC-65 and decided to measure the caps 'in circuit' - using a technique with a signal gen, a variable series resistor, a 10x amplifier and a DMM. The purpose of the amplifier was so I only needed to apply 25mV P-P from the signal gen and still be able to get an accurate reading on the DMM, the series resistor was set to match the resistance in parallel with the caps. This so I could measure the signal drop when probing the cap on the PCB. I could use 20Khz sine wave to get good readings on the DMM and i.e. swapping the probes over the caps only changed the reading about 10%. So here are the measured/calculated caps values: C5 = 2n2 C6 = 1n (hey! I guessed it) C8 = 2n2 C11 = 22n C14 = 27n I cannot swear by these values but they're likely better than ball park figures. Spice Simulation to follow... |
| dcac:
Here's the spice simulation - in high gain mode (6.5A) BW is about 23KHz - and in low gain (65A) about 34KHz. High gain Low gain I have no spice model for the hall sensors so these are just simulated with sine generators with 500 ohms output impedance. Do we know anything more specific about these sensors other than they appear to be in sot-143 size? |
| dcac:
While I had my 10x amplifier handy I tried to measure the signal directly from the hall sensors - between pin 1-3 on HALL 1. My amp can also be set to 100x and is based on OP37 so it has quite low noise and BW is about 250KHz. The hall sensors seems to have allot of noise however - about 100uV P-P - but it wasn’t an easy measurement as CC-65 has no shielding to speak of - so I really had to fight with the 50Hz mains pickup. It’s interesting there seem to be frequency peaking already at the hall input formed by R11//C13. When measuring 50mA RMS with the clamp I got: 500Hz = 120uV 1KHz = 123uV 5Khz = 132uV 10Khz = 153uV 20Khz = 214uV RMS from the hall sensors. This is then amplified about 50x by the 272s in high gain mode and about 5x in low gain. |
| Elasia:
Yeah it has no shielding at all practically... picks up damn near anything, even the earth lol |
| dcac:
I wonder why they chosen to frequency limit the 272s - well, they're limited with C5-C6 - but then peaking is applied with C8 and C14. I will try a simulation later without the caps. Also why does U3-1-2 not have symmetrical feedback resistors R22 and R15 - one is 11K the other 7.5K. |
| Navigation |
| Message Index |
| Next page |
| Previous page |