Fluke Voltage Standard

[JohnS_AZ]

I'm really just curious ....

I've been cleaning up my shop and came across this Fluke 510A AC reference standard. It puts out 2400Hz AC at 10 volts. I don't even remember where I got it, probably in a mixed lot at an auction. My question, who the heck needs needed a super-accurate source of 2400 Hz??  If it were 400 Hz I could guess avionics, but I don't have a clue for this.

BTW ... I scoped the output and it's a -very- clean sinewave, and my frequency counter said 2.400013 KHz.

[RayJones]

The old analogue fax machines used a 2400Hz carrier, and synchronisation of motor speeds at each end was often based about the carrier frequency.

If you were off speed, the image would be skewed as the paper was fed out during the image.

300Hz Start tones, 450Hz stop tones, and from memory 600Hz was the start tone for double speed paper feed.
Those were my earliest days in paid electronics, and honestly they are not missed  .

[RayJones]

Scratch 600Hz, it was a 675Hz start tone for double the feed speed.

600Hz didn't sit right, especially since the 2nd harmonic from 300Hz tone could have easily tripped the tone detector for double speed mode, so that's why 675Hz was chosen.

According to wikipedia, Group 1 fax used the 300Hz start tone and took 6 minutes to send a page, Group 2 used the 675Hz start tone and took 3 minutes to send a page, and Group 3 was the first of the digital faxes which then employed compression techniques to speed the image delivery (delta compression from memory).

[saturation]

Its at minimum, a metrology quality, for best AC reference.

According to the Fluke site, it was made around 1970s, and has a rated accuracy Vac of 0.01%, whereas the current AC standard 5790a by Fluke is 0.002%, about 5x more accurate.

If I owned this, I'd use it to calibrate my DMM AC ranges.  The fact is works near spec 40 years later is fantastic.   Given many DMM are calibrated to 0.1% Vac this device still is very relevant today.

[Rhythmtech]

Here's a spec sheet I found

I would think from the description that it's a voltage reference that was used to calibrate volt meters prior to digital equipment where the frequency was less important to the reading value.

[Zero999]

I wonder what topology it uses for an oscillator?

If I were to design it, I would go for digital (crystal controlled clock, counter or MCU, EEPROM and DAC) but this is back in the 70s when that sort of design wasn't so common.

Another method would be a crystal clock, counter and a filter to convert the squarewave to a sine for low frequencies (say below 10kHz) and a sinusoidal crystal oscillator and a buffer amplifier for higher frequencies.

[NiHaoMike]

It might have been designed for use in telecom. 2400Hz is about right for some signaling frequency on an analog phone line. (2600Hz was the famous one since that was once used by hackers.)

[saturation]

The schematic is fairly detailed and the manual on the Fluke website is a scanned copy of a paper one, has a layout almost like an HP manual.  To add flavor it has human signatures and approval stamps all dating between 1971-2.

The chips are very generic, and my take on it is its very easy to service with today's ordinary electronic test equipment.

I wonder what topology it uses for an oscillator?

If I were to design it, I would go for digital (crystal controlled clock, counter or MCU, EEPROM and DAC) but this is back in the 70s when that sort of design wasn't so common.

Another method would be a crystal clock, counter and a filter to convert the squarewave to a sine for low frequencies (say below 10kHz) and a sinusoidal crystal oscillator and a buffer amplifier for higher frequencies.

[JohnS_AZ]

Since you guys seemed interested, I took a few more pictures.

First is under the top cover.
Second is also under the top cover but with the metal shield (center) removed.
Third is under the bottom cover.

The thing that caught my eye were the two incad. light bulbs (far left, second picture) They align with two small unlabeled holes in the BACK panel of the unit. Also the small board in the bottom that obviously sets the 2400Hz frequency. I also wonder about the large flat white device just to the left of the shielded section. SAW filter maybe? I should go find the schematic.

[Mechatrommer]

the real classic porn! whats the middle circuit in middle picture? (with circle oscillator and was shielded) looks like a radio transmitter to me

[slburris]

The thing that caught my eye were the two incad. light bulbs (far left, second picture) They align with two small unlabeled holes in the BACK panel of the unit. Also the small board in the bottom that obviously sets the 2400Hz frequency. I also wonder about the large flat white device just to the left of the shielded section. SAW filter maybe? I should go find the schematic.

The schematic I have seems to show a single lightbulb across the low voltage AC supply.
The manual I have seems very similar to your unit, but not identical.  The second
board doesn't have the white device, but seems to have most of the other components.

The full manual is too big to attach to eevblog, so I stuck it on my site:

http://electroscott.com/510A_AA_imeng0000.pdf
Scott

[saturation]

Awesome pics, again looks very easy to maintain at home for a lifetime.

Since you guys seemed interested, I took a few more pictures.

First is under the top cover.
Second is also under the top cover but with the metal shield (center) removed.
Third is under the bottom cover.

The thing that caught my eye were the two incad. light bulbs (far left, second picture) They align with two small unlabeled holes in the BACK panel of the unit. Also the small board in the bottom that obviously sets the 2400Hz frequency. I also wonder about the large flat white device just to the left of the shielded section. SAW filter maybe? I should go find the schematic.