#### Trying to understand the 453 calibrator

Richard P

I’ve always been able to get a good 1 kc square wave from the front panel BNC calibrator output. Works ok for compensating a probe. But I never could get the 1 kc signal from the probe loop on the side panel. Today, I verified the signal is being delivered to one side of the loop through parallel resistors equaling 20 ohms, in agreement with the schematic. But since the other side of the loop is tied to ground, also in agreement with the schematic, it seems to me the square wave is going to ground, and hence, that is why I have never seen any square wave on the loop. Never, ever. The loop is a ground. How is this supposed to work? Thanks.

Richard

Bob Albert

It's not delivering a square wave of voltage.  It's a current loop for calibrating a current probe.
Bob

On Monday, August 3, 2020, 10:12:11 AM PDT, Richard P via groups.io <wb5nen=yahoo.com@groups.io> wrote:

I’ve always been able to get a good 1 kc square wave from the front panel BNC calibrator output. Works ok for compensating a probe. But I never could get the 1 kc signal from the probe loop on the side panel. Today, I verified the signal is being delivered to one side of the loop through parallel resistors equaling 20 ohms, in agreement with the schematic. But since the other side of the loop is tied to ground, also in agreement with the schematic, it seems to me the square wave is going to ground, and hence, that is why I have never seen any square wave on the loop. Never, ever.  The loop is a ground. How is this supposed to work? Thanks.

Richard

Richard P

Ahhhh. That’s above my pay grade, I suppose. I just thought you used the little bar to compensate a basic probe.

SCMenasian

It's to calibrate a current probe. A calibrated current square wave is in the loop. A clip-on current probe should pick it up.

Harvey White

It's a current loop for calibrating current probes.

Harvey

On 8/3/2020 1:12 PM, Richard P via groups.io wrote:
I’ve always been able to get a good 1 kc square wave from the front panel BNC calibrator output. Works ok for compensating a probe. But I never could get the 1 kc signal from the probe loop on the side panel. Today, I verified the signal is being delivered to one side of the loop through parallel resistors equaling 20 ohms, in agreement with the schematic. But since the other side of the loop is tied to ground, also in agreement with the schematic, it seems to me the square wave is going to ground, and hence, that is why I have never seen any square wave on the loop. Never, ever. The loop is a ground. How is this supposed to work? Thanks.

Richard

Harvey White

It depends on the scope.

On a 7000 series scope, the bar is insulated and there's a separate calibrator BNC.  Use whichever you need.

The closest I can get to a 453 is one of my 468 scopes, where I didn't see a calibrator BNC (very quick look), did see a bare wire loop.  That wire loop was labeled with a current and voltage.  You can get that if the wire loop goes to the source, then is grounded through a current limiting resistor for the current probe.  I think that the voltage was roughly 200 mv p-p.

If the loop is directly grounded, all it can provide is a current, and you'll find the calibrator output elsewhere.

Harvey

On 8/3/2020 1:25 PM, Richard P via groups.io wrote:
Ahhhh. That’s above my pay grade, I suppose. I just thought you used the little bar to compensate a basic probe.

Richard P

Harvey (and all),

Yeah, my loop is directly grounded, so I will get my calibration voltage signal from the BNC on the front panel. Works fine.

R

Colin Herbert

There is a bit of a clue in that the calibration loop on the right-hand side is marked with an arrow pointing left and the words "5mA" followed by a square-wave. The calibration BNC on the front panel is marked "1 kHz". This should lead one to think that the BNC on the front-panel is for Time/Div calibration and the loop on the right side is for Current/Div calibration. I will have to look at how the "1kHz" is generated to see if it really is accurate (most of these are not that accurate).
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Richard P via groups.io
Sent: 03 August 2020 19:02
To: TekScopes@groups.io
Subject: Re: [TekScopes] Trying to understand the 453 calibrator

Harvey (and all),

Yeah, my loop is directly grounded, so I will get my calibration voltage signal from the BNC on the front panel. Works fine.

R

Colin Herbert

Aha! I should have looked more closely. The calibration BNC on the front panel is indeed a voltage calibration and is switchable between 1V and 0.1V by means of a switch on the side-panel. Silly me!

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Colin Herbert via groups.io
Sent: 03 August 2020 19:22
To: TekScopes@groups.io
Subject: Re: [TekScopes] Trying to understand the 453 calibrator

There is a bit of a clue in that the calibration loop on the right-hand side is marked with an arrow pointing left and the words "5mA" followed by a square-wave. The calibration BNC on the front panel is marked "1 kHz". This should lead one to think that the BNC on the front-panel is for Time/Div calibration and the loop on the right side is for Current/Div calibration. I will have to look at how the "1kHz" is generated to see if it really is accurate (most of these are not that accurate).
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Richard P via groups.io
Sent: 03 August 2020 19:02
To: TekScopes@groups.io
Subject: Re: [TekScopes] Trying to understand the 453 calibrator

Harvey (and all),

Yeah, my loop is directly grounded, so I will get my calibration voltage signal from the BNC on the front panel. Works fine.

R

Harvey White

The calibrator square wave is intended to be a voltage reference and not a time reference, not in the early scopes.  For a scope with a microprocessor in it, it can be derived from the processor clock, for a scope with lots of digital electronics, generally from a master oscillator.  In addition, it's used to help adjust the HF compensation of a probe.

For an interesting exercise, experiment with the output of a function generator doing pulses (or pulse generator, of course) and then adjust and misadjust the HF compensation on the probe.  I found interesting results.  The PRF of the pulse and the duration are significant.

Harvey

On 8/3/2020 2:21 PM, Colin Herbert via groups.io wrote:
There is a bit of a clue in that the calibration loop on the right-hand side is marked with an arrow pointing left and the words "5mA" followed by a square-wave. The calibration BNC on the front panel is marked "1 kHz". This should lead one to think that the BNC on the front-panel is for Time/Div calibration and the loop on the right side is for Current/Div calibration. I will have to look at how the "1kHz" is generated to see if it really is accurate (most of these are not that accurate).
Colin.

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] On Behalf Of Richard P via groups.io
Sent: 03 August 2020 19:02
To: TekScopes@groups.io
Subject: Re: [TekScopes] Trying to understand the 453 calibrator

Harvey (and all),

Yeah, my loop is directly grounded, so I will get my calibration voltage signal from the BNC on the front panel. Works fine.