EEVblog Electronics Community Forum

Products => Test Equipment => Topic started by: PaulAm on August 10, 2022, 01:21:56 pm

Title: Fluke 8840 Option 9 board
Post by: PaulAm on August 10, 2022, 01:21:56 pm

This is not my project, but since there seems to be a lot of interest in the 8840 I thought I'd post this.

A member of the Fluke-DMM groups.io list has recreated the Option 9 AC converter board.  All Kicad files are available for download from his project page:

https://www.dudley.nu/projects/Fluke_8840A/ (https://www.dudley.nu/projects/Fluke_8840A/)

Looks like some nice work.

Title: Re: Fluke 8840 Option 9 board
Post by: Kleinstein on August 10, 2022, 07:17:56 pm

The JFETs for switching should not be very critical, but the J109 looks like rather high in capacitance. I would consider a more standard PN4393 or J113.

To get a little more withstand voltage for the reed relay at the input, one could consider a photomos switch in series.
There are quite some resistors that effect the gain. The absolute accuracy would likely not matter and could likely be trimmed, but the stabiltiy could be an issue.
Some of the small compensation capacitors would likely depend on the layout and resistor types for parasitic capacitance. So the best values may change a little.