How do I find out the capacitance of a BNC connector channel on an oscilloscope?

[Bubble-Flow]

I am using a piezo hydrophone connected to an oscilloscope. In order to convert the signal displayed in volt on the oscilloscope to bar, the manufacturer has provided the formula on the attached pic.

According to the explanation it should be either 13 or 50 but on the tektronix tds 210 I am using, nothing is stated. Nowhere on the data sheet or manual can I find the capacity of the BNC connector either. Where do I get this information from or is this not relevant and I am somehow not understanding the formula  . Please help!


Thanks for reading!

[CaptDon]

Most Tek stuff is marked right at the connector such as 10m/15pf meaning 10 megaohms shunted by 15 picofarads. The manual should most definitely state the input impedance. Some of those little handy scopes have probes attached that can't be removed and even those stated the resistance and capacitance right on the probe.
Best wishes. Look at the page where the vertical channel frequency response and sensitivity settings are listed.

[mindcrime]

I was confused as hell by this at first. So is "capacity" a synonym for "capacitance" then? I've never heard "capacity" used that way before...

[TimFox]

In this context, “capacity” is a mistake.  Tho only English technical term for C in the equation is “capacitance”, measured in Farads.  “Capacity” is a perfectly good word for other concepts.

[ebastler]

I was confused as hell by this at first. So is "capacity" a synonym for "capacitance" then? I've never heard "capacity" used that way before...

Probably just a translation error. Is that a German hydrophone by any chance? In German, the same word (Kapazität) is used for both, capacity and capacitance.

[mindcrime]

I was confused as hell by this at first. So is "capacity" a synonym for "capacitance" then? I've never heard "capacity" used that way before...

Probably just a translation error. Is that a German hydrophone by any chance? In German, the same word (Kapazität) is used for both, capacity and capacitance.

Ah, that would make sense. Had me going there for a sec, because when I think "capacity" in an electrical / electronics context, my mind immediately goes to "current carrying capacity" which would be something quite different!

[Vovk_Z]

Here is a screen-shot from TDS200 series User Manual (Appendix A. Specifications):

[David Hess]

You can also measure it with a normalizer and square wave source.  Put a 1 megohm resistor in series with the input and a small 10 to 20 picofarad variable capacitor in parallel with the resistor.  When driven with a low frequency square wave source, adjust the variable capacitor for a square waveform.  Now the variable capacitor has the same value as the input capacitance and can be easily measured.

[Bubble-Flow]

Here is a screen-shot from TDS200 series User Manual (Appendix A. Specifications):

Is 20 pF the capacitance of the BNC connector?
I am not sure becacuse I have a found a universal manual for the TDS 200 series, which states that the input capacitance on 10x and 1x position are 14,5 and 80 pF respectively. I have attached a scrrenshot from the maual. I am a bit confused. Which information is the recorder input capacitance?
Also how do I know which position I am using? 10x or 1x? Is this a parameter in the settings I have to adjust?

[Bubble-Flow]

I was confused as hell by this at first. So is "capacity" a synonym for "capacitance" then? I've never heard "capacity" used that way before...

In this context, “capacity” is a mistake.  Tho only English technical term for C in the equation is “capacitance”, measured in Farads.  “Capacity” is a perfectly good word for other concepts.

Yes, apparently they mean capacitance by "capacity" here. Thanks for mentioning it. I was also confused and couldn't find any information about "capacity" anywhere. I corrected the title of the question.

I was confused as hell by this at first. So is "capacity" a synonym for "capacitance" then? I've never heard "capacity" used that way before...

Probably just a translation error. Is that a German hydrophone by any chance? In German, the same word (Kapazität) is used for both, capacity and capacitance.

Yes, the hydrophone is by a german manufacturer. That's probably why there is a mistranslation in the manual!   

[Bubble-Flow]

Here is a screen-shot from TDS200 series User Manual (Appendix A. Specifications):

Is 20 pF the capacitance of the BNC connector?
I am not sure becacuse I have a found a universal manual for the TDS 200 series, which states that the input capacitance on 10x and 1x position are 14,5 and 80 pF respectively. I have attached a scrrenshot from the maual. I am a bit confused. Which information is the recorder input capacitance?
Also how do I know which position I am using? 10x or 1x? Is this a parameter in the settings I have to adjust?

Nevermind! I Just figured out I had posted the specs of the P2100 probe not the actual oscilloscope. 20 pF is correct!

Thanks everyone

[Vovk_Z]

I have a found a universal manual for the TDS 200 series, which states that the input capacitance on 10x and 1x position are 14,5 and 80 pF respectively. I have attached a scrrenshot from the maual. I am a bit confused. Which information is the recorder input capacitance?

1. 14.5pF is the property of a probe. It is clearly stated there.
It means that for an external circuit a probe is like a 14.5 pF capacitor.

Also how do I know which position I am using? 10x or 1x? Is this a parameter in the settings I have to adjust?

I am a bit confused here too :-). You switch it to either 10:1 (the most used) or 1:1. Nobody other. If somebody other works with it - you can look at a probe switch and find in which position it is.
PS: we compensate the probe only in 10:1 position. There is nothing to compensate in 1:1.