Products > Test Equipment

HP3478A Questions

(1/2) > >>

PixieDust:
Hi guys!

I'm reading the service manual for the HP3478 and I'm having some difficulty understanding a few things.

http://www.arimi.it/wp-content/Strumenti/HP/Multimetri/hp-3478a-Service.pdf

On page 11 of the pdf, or page 1-2, we see Table 1-1 Specifications.

Questions:

1.) Under DC Voltage, the "Maximum Input Voltage" is stated as "Hi to Lo: 303V rms or 450V peak". Why is it just +ve 450V? In the line below, we see +/-500V. Typo? In the "Input Characteristics" we see +/-303.099V as the maximum reading, so it seems like it should +/- 450V no?

2.) What does the second line "Maximum Input Voltage" mean? What is this "Hi or Lo to Earth Ground"?

HKJ:

--- Quote from: PixieDust on November 04, 2022, 09:37:51 am ---1.) Under DC Voltage, the "Maximum Input Voltage" is stated as "Hi to Lo: 303V rms or 450V peak". Why is it just +ve 450V? In the line below, we see +/-500V. Typo? In the "Input Characteristics" we see +/-303.099V as the maximum reading, so it seems like it should +/- 450V no?

2.) What does the second line "Maximum Input Voltage" mean? What is this "Hi or Lo to Earth Ground"?

--- End quote ---

I do not see the problem, the input can handle up to 450V peak or DC before damage, and the meter can show readings up to 303V, i.e. from 303 to 450 the meter will not show correct (It will probably either show 303 or overload), but the meter will not be damaged.

The isolation between the electronic and the box (i.e. Earth Ground) can handle up to 500V and that is the same from either input terminal.

PixieDust:

--- Quote from: HKJ on November 04, 2022, 09:55:24 am ---I do not see the problem, the input can handle up to 450V peak or DC before damage, and the meter can show readings up to 303V, i.e. from 303 to 450 the meter will not show correct (It will probably either show 303 or overload), but the meter will not be damaged.

--- End quote ---

Yep, I understand the second bit. I just wasn't sure why they left out the +/- sign in front of 450V whereas they used it everywhere else. Surely probing things back to front wouldn't result in a blown meter! Would happen so often!


--- Quote from: HKJ on November 04, 2022, 09:55:24 am ---The isolation between the electronic and the box (i.e. Earth Ground) can handle up to 500V and that is the same from either input terminal.

--- End quote ---

This I still don't understand.

HKJ:

--- Quote from: PixieDust on November 04, 2022, 11:29:28 pm ---
--- Quote from: HKJ on November 04, 2022, 09:55:24 am ---I do not see the problem, the input can handle up to 450V peak or DC before damage, and the meter can show readings up to 303V, i.e. from 303 to 450 the meter will not show correct (It will probably either show 303 or overload), but the meter will not be damaged.

--- End quote ---

Yep, I understand the second bit. I just wasn't sure why they left out the +/- sign in front of 450V whereas they used it everywhere else. Surely probing things back to front wouldn't result in a blown meter! Would happen so often!

--- End quote ---

The meter is rated to show +/- voltage, i.e. the sign is already implied in the range.


--- Quote from: PixieDust on November 04, 2022, 11:29:28 pm ---
--- Quote from: HKJ on November 04, 2022, 09:55:24 am ---The isolation between the electronic and the box (i.e. Earth Ground) can handle up to 500V and that is the same from either input terminal.

--- End quote ---

This I still don't understand.

--- End quote ---

Not all voltages are measured relative to ground, sometimes you need to measure a voltage on top of another voltage and in these cases the total voltage must not be above 500V, i.e. you cannot measure a 5V supply is on top of a 600V supply like: 0V / 600V / 605V, but you could if the connections was: -600V / 0V / 5V  (It is the same voltages, but ground is connected different).
All meters has this rating, on handheld it is often the same as maximum input voltage, but bench meters are different.

PixieDust:

--- Quote from: HKJ on November 05, 2022, 08:43:35 am ---The meter is rated to show +/- voltage, i.e. the sign is already implied in the range.

--- End quote ---

Understood, thanks.


--- Quote from: HKJ on November 05, 2022, 08:43:35 am ---Not all voltages are measured relative to ground, sometimes you need to measure a voltage on top of another voltage and in these cases the total voltage must not be above 500V, i.e. you cannot measure a 5V supply is on top of a 600V supply like: 0V / 600V / 605V, but you could if the connections was: -600V / 0V / 5V  (It is the same voltages, but ground is connected different).
All meters has this rating, on handheld it is often the same as maximum input voltage, but bench meters are different.

--- End quote ---

Thanks. I haven't bumped into things like this yet, so I'll keep in mind as I continue on my electronics journey.

Navigation

[0] Message Index

[#] Next page

There was an error while thanking
Thanking...
Go to full version
Powered by SMFPacks Advanced Attachments Uploader Mod