Hi all,
I was yesterday using the hps140i and found that when the probe its connected only to ground gives me a sine wave.
In order of a few mv but its a perfect sine. If i touch the probe hook the signal increase.
Its this a problem on my design or my scope its dying?
thanks
The probe is picking up the 60 Hz (or 50 Hz) powerline/mains frequency. When you touch the probe your body behaves as an antenna picking up a stronger version of the same signal…
that means what? Its normal? a problem on my power supply?
Im using a bipolar ps.
This is normal
hum… ok.
Its a bit annoying.
Adding some bypass caps will help?
Its this what produce the mains hums (ground loop) ?
It is quite normal, and is an indication that the instrument is doing what it is supposed to–I.e. it is a sensitive, high-impedance input instrument. Adding anything to “fix” it will affect the 'scope’s accuracy and usefulness.
Here is a trace captured on a $3800 Lecroy oscilloscope, using a 300MHz Tektronix probe (at 1:1) with just the ground lead connected. Note the 60 Hz dominant frequency (the US mains frequency) carrying numerous other higher frequencies the probe (behaving as an antenna) has “picked-up”; the pk-pk amplitude is 5.20 mV:
Here is the same probe, same connections, with me touching the probe tip. The 60 Hz dominant frequency remains however the pk-pk amplitude is now 1.30 V. Note also the my body capacitance has filtered much of the higher frequency elements:
There is nothing to fix, it is just the nature of oscilloscopes. Once a signal to be observed has been properly probed this ambient “noise” will become insignificant…
Electronic its really impressive 
Thanks all.
