Question about uni-t 81b mode x1 and x10 with oscilloscope probe HP-3060 - Page 1
Forum section: electronics / beginners

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: June 06, 2018, 11:05:41 pm
content: Hi there.I'm a super fresh new user and this was a post from the review of this particular MeterI've bought once in 2008 an UT81B and worked fine for graphing signals from microcontrollers ( Arduino, Microchip, NXP, etc) and then i sell it cause i stop the electronics and do some stuff on Embedded Linux, becaming a software guy.Now im going back to electronics and i have reorder a brand new uni-t 81B, which i kind like because its handy, simple to use on troubleshooting microcontrolers signals and now Linux SBC's. Its like a old Game Boy in terms of consumption, so i use recharchable batteries and 2000mA gave more or less 10 hours with low brightness ( 3) and contrast around 10. However i don't remember what mode was the proper mode of the oscilloscope probe ( x1 or x10) for direct measuring. In x10 the 1KHz signal generated from a Arduino ( Fast PWM mode) became attenuated with a probe model HP-3060 and the scope does not have option for the x1 and x10 modes... I should have take notes... Dumb meI'll post photos soon

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: June 09, 2018, 10:36:57 pm
content: Hi i think i can test the scope with a function generator and maybe get more accurate conclusions, since it has a fixed impedance of 50Ohms. It has been done quite a lot of reviving electronics and solving problems

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: June 11, 2018, 09:22:33 pm
content: Before i tested the uni-t 81b and the probe, i was thinking and remembering about the input impedances, more likely the resistor divider created between the input voltage multimeter and the x10 mode probe, using a 5VDC source, it gives almost 1.96V which is near the values of the 8.53MOhm of the probe and the 10M in volt mode.The other thing is the added capacitance to the scopemeter voltage input which acts like a integrator for small frequencies ( around 101pF), small signals, but usable for higher frequencies ( above 800Khz). If using mains ( using a isolated transformer ) with x10 it works fine since its out of the band of the capacitve network.So it is direct measure with x1 for small signal , no exceding the Maximum ratings of the probe and hence the scopemeter, and x10 for higher voltages ( example 230V), which matches the specs of this probe .I need to review some of the electronics that i have learn in the past, but today no need for instruments, just using basic stuff reminder.

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: June 11, 2018, 10:53:41 pm
content: Here is an example with direct probes and x10 probe with 230V / 117V travel adapter transformer for isolating from mains and using a smaller AC voltage, power. The ratio of the x10 probe plus the input of the scope is about 2.7, since it gave 43VAc rms.So the scope has fixed 10MOhm impedance, the probe is about 6.3Mohm impedance at that voltage / frequency in terms of resistive divider.The same ratio also applies for 230Vac.

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: June 13, 2018, 08:46:53 am
content: I just measured yesterday the DC impedance of the probe and it is 8.53 MOhm, so if we redo the calculations for resistor dividor between probe and scope it would give 14.5 ~14.67MOhm for the impedance of the scope, using the same ratio of 2.7 mentioned above ( 117V / 43V RMS)So the x10 mode is usable for AC mains volts, using a isolation transformer , within the spec of CATII 300V of the probe. The probe itself came with a insulation cap to seal the ground and let a little contact of the tip exposed.I'll post a video of the setup measurement.

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: June 13, 2018, 10:13:57 am
content: Quote from: malagas_on_fire on June 13, 2018, 08:46:53 am

author: malagas_on_fire
author_rank: Frequent Contributor
timestamp: June 13, 2018, 10:09:18 pm
content: Hi there.I think i missed the photo about the probe in x1 mode using the same setup for the x10 mode to show the ratio. I tried on a flat 9V battery and i get the same ratio ( 2.7 = Vx10/Vx1)But watch what appends when i plug to an arduino with timer 1 configured for 1KHz / 50% dutty cycle: x1 OK, x10 kind of Triangle wave plus dc offset... Well some capacitance integration is going on maybe due to the circuitry with compensation caps plus the impedance of the scope.The one thing that i remeber was seeing the video were David Jones talks about probing techniques and i end to stick the oscilloscope probe positive on P10 and connect a wire to GND, resulting in a more pure triangle wave with the same offset. I've learn something from this experience has well the video .Thanks a lot