PicoScope 7 Software
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Picoscope probes picking up a very noticeable 50 Hz signal
Picoscope probes picking up a very noticeable 50 Hz signal
Dear all,
I recently bought a new Picoscope 2204A.
I'm currently trying to use it in a small project involving a BPW34 photodiode, trying to build a custom monitor PWM detector.
However, I noticed that the probes (I have the TA208 kit, which was included together with the Piscoscope) are always picking up a noticeable 50 Hz noise, even when there is nothing connected to them.
In particular, if I just connect a probe to one of the channels, and set the probe type to "10x", without connecting or touching anything, I can see a 50 Hz signal ranging from around -100 mV to 100mV (or similar values, as in the attached screenshot).
If I touch the tip of the probe, this signal I'm picking up is amplified a lot and the readings range from around -22V to 22V.
If instead I touch the ground lead tip only, this signal is reduced a lot, and I can see it ranging from around -14 mV to 14 mV (experiencing an almost 10 times reduction).
If I set the Picoscope 6 software as if I was using a "1x" probe, all these readings are divided by 10.
Is it normal? Do you know why I'm observing such a high unwanted 50 Hz noise?
Thank you very much in advance.
Regards,
Francesco
I recently bought a new Picoscope 2204A.
I'm currently trying to use it in a small project involving a BPW34 photodiode, trying to build a custom monitor PWM detector.
However, I noticed that the probes (I have the TA208 kit, which was included together with the Piscoscope) are always picking up a noticeable 50 Hz noise, even when there is nothing connected to them.
In particular, if I just connect a probe to one of the channels, and set the probe type to "10x", without connecting or touching anything, I can see a 50 Hz signal ranging from around -100 mV to 100mV (or similar values, as in the attached screenshot).
If I touch the tip of the probe, this signal I'm picking up is amplified a lot and the readings range from around -22V to 22V.
If instead I touch the ground lead tip only, this signal is reduced a lot, and I can see it ranging from around -14 mV to 14 mV (experiencing an almost 10 times reduction).
If I set the Picoscope 6 software as if I was using a "1x" probe, all these readings are divided by 10.
Is it normal? Do you know why I'm observing such a high unwanted 50 Hz noise?
Thank you very much in advance.
Regards,
Francesco
- Attachments
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Re: Picoscope probes picking up a very noticeable 50 Hz signal
have you connected the ground clip of the probe to the ground your project ?
Benno
Benno
Re: Picoscope probes picking up a very noticeable 50 Hz signal
Hello,
I'm very sorry for the big delay in replying you, but I was away for work and I was not able to try before today.
I was actually testing the probe as it was, without connecting it to any project or other circuit, and that was the case in which I was observing it picking up that noticeable 50 Hz noise.
I then tried following this discussion, together with this other one (section related to the BPW34S photodiode); in the first, in particular, the user "KM" is using a Picoscope 2204A.
However, other than not being able to see any PWM (the voltage I read is always too low or too disturbed, if compared to the results they are getting, even if I use a 9V battery or two 1.5V batteries in series - but thay is probably due some wrong configuration in my circuit), I can still see some small disturbance being picked up, even if is now much smaller and especially when there is low light hitting the photodiode surface and the probe is set to '1x'.
This noise seems again to be at a frequency around 50 Hz, as in the attached screenshot.
Is it my environment which is too "polluted"? Is there something wrong which I am doing when setting up the oscilloscope and/or connecting the probe or is this noise actually expected (I'm not an expert at all and I'm currently trying to understand if my setup is wrong and why)? A picture of my circuit setup is attached too.
Thank you very in advance for your assistance.
Regards,
Francesco
I'm very sorry for the big delay in replying you, but I was away for work and I was not able to try before today.
I was actually testing the probe as it was, without connecting it to any project or other circuit, and that was the case in which I was observing it picking up that noticeable 50 Hz noise.
I then tried following this discussion, together with this other one (section related to the BPW34S photodiode); in the first, in particular, the user "KM" is using a Picoscope 2204A.
However, other than not being able to see any PWM (the voltage I read is always too low or too disturbed, if compared to the results they are getting, even if I use a 9V battery or two 1.5V batteries in series - but thay is probably due some wrong configuration in my circuit), I can still see some small disturbance being picked up, even if is now much smaller and especially when there is low light hitting the photodiode surface and the probe is set to '1x'.
This noise seems again to be at a frequency around 50 Hz, as in the attached screenshot.
Is it my environment which is too "polluted"? Is there something wrong which I am doing when setting up the oscilloscope and/or connecting the probe or is this noise actually expected (I'm not an expert at all and I'm currently trying to understand if my setup is wrong and why)? A picture of my circuit setup is attached too.
Thank you very in advance for your assistance.
Regards,
Francesco
- Attachments
-
Re: Picoscope probes picking up a very noticeable 50 Hz signal
can you post a picture or photo of your test setup ?
Benno
Benno
Re: Picoscope probes picking up a very noticeable 50 Hz signal
Hello,
I'm sorry! I thought I had posted it too, but I probably forgot to add it as an attachment.
This picture shows one of the setups I tested, which were all very similar (with a 10 kOhm resistor and the BWP34 photodiode), but for the battery (I tested without battery, with a 1.5V one, with two 1.5V batteries in series and with one 9V battery).
Today, doing again some tests and thanks to some suggestions I got from the LEDStrain forum, I was able to build a much more working circuit, without battery and with a 100 kOhm resistor: Circuit setup photo.
What I notice now is that the noise, even when the probes are set to '1x', is much more reduced, but it becomes again quite noticeable if I touch the photodiode and, even worse, the 100 kOhm resistor's ends:
Picture of Picoscope showing the 50 Hz noise.
Instead, if I try to measure the PWM of my ASUS phone, I get a much cleaner result than all my previous attempts, but there is still some high frequency noise being picked up, which is, in any case, not always observed (especially when trying to test other devices):
Picoscope reading when testing my ASUS phone.
I'm sorry for all the single links, but I can't seem to be able to post more than one image, either as attachment or as "[img]", as, if I do so, when I click "Submit", unfortunately, the post is not submitted and the page gets stuck while loading (I don't know why, I tried few times but without success).
Thank you very much in advance.
Regards,
Francesco
I'm sorry! I thought I had posted it too, but I probably forgot to add it as an attachment.
This picture shows one of the setups I tested, which were all very similar (with a 10 kOhm resistor and the BWP34 photodiode), but for the battery (I tested without battery, with a 1.5V one, with two 1.5V batteries in series and with one 9V battery).
Today, doing again some tests and thanks to some suggestions I got from the LEDStrain forum, I was able to build a much more working circuit, without battery and with a 100 kOhm resistor: Circuit setup photo.
What I notice now is that the noise, even when the probes are set to '1x', is much more reduced, but it becomes again quite noticeable if I touch the photodiode and, even worse, the 100 kOhm resistor's ends:
Picture of Picoscope showing the 50 Hz noise.
Instead, if I try to measure the PWM of my ASUS phone, I get a much cleaner result than all my previous attempts, but there is still some high frequency noise being picked up, which is, in any case, not always observed (especially when trying to test other devices):
Picoscope reading when testing my ASUS phone.
I'm sorry for all the single links, but I can't seem to be able to post more than one image, either as attachment or as "[img]", as, if I do so, when I click "Submit", unfortunately, the post is not submitted and the page gets stuck while loading (I don't know why, I tried few times but without success).
Thank you very much in advance.
Regards,
Francesco
Re: Picoscope probes picking up a very noticeable 50 Hz signal
Hello,
Sorry, I just noticed that the picture of my initial circuit setup did not get attached again.
This one should be the right picture: initial circuit setup.
Thank you!
Sorry, I just noticed that the picture of my initial circuit setup did not get attached again.
This one should be the right picture: initial circuit setup.
Thank you!
Re: Picoscope probes picking up a very noticeable 50 Hz signal
Ciao Francesco,
The noise you are seeing is not a fault of your picoscope device.
Your breadboard circuit shows some long wiring, which forms large loops and the so-called "hum" you are seeing on your picoscope are voltages induced by the 50 Hz power line present in your area.
My recommendation to you is to do some background reading, such as the "ABC of probes" from tek.com/document/primer/abcs-probes-primer - page 49 provides a pretty good explanation of the observed effect.
Practical hint: Use the shortest "jump wires" possible when breadboarding, and turn off any power electronics in close proximity to your circuit such as lamps, monitors, power supplies etc. when probing.
Also, disregard the probe's ground clip cable when possible. Pull off the hook and connect your circuit "ground" directly to the probe's ground sleeve.
This shall significantly reduce the induced voltages.
Cheers,
JoeD.
The noise you are seeing is not a fault of your picoscope device.
Your breadboard circuit shows some long wiring, which forms large loops and the so-called "hum" you are seeing on your picoscope are voltages induced by the 50 Hz power line present in your area.
My recommendation to you is to do some background reading, such as the "ABC of probes" from tek.com/document/primer/abcs-probes-primer - page 49 provides a pretty good explanation of the observed effect.
Practical hint: Use the shortest "jump wires" possible when breadboarding, and turn off any power electronics in close proximity to your circuit such as lamps, monitors, power supplies etc. when probing.
Also, disregard the probe's ground clip cable when possible. Pull off the hook and connect your circuit "ground" directly to the probe's ground sleeve.
This shall significantly reduce the induced voltages.
Cheers,
JoeD.
Re: Picoscope probes picking up a very noticeable 50 Hz signal
Dear JoeD,
Thank you very much for your detailed and kind reply!
I will surely try out your practical hints and read the "ABC of probes" section you suggested.
I actually ordered some much shorter jump wires for this small project, in order to try them out instead of the longer ones I was using before.
Thank you again for your assistance.
Regards,
Francesco
Thank you very much for your detailed and kind reply!
I will surely try out your practical hints and read the "ABC of probes" section you suggested.
I actually ordered some much shorter jump wires for this small project, in order to try them out instead of the longer ones I was using before.
Thank you again for your assistance.
Regards,
Francesco