https://github.com/openscopeproject/keithley1950

Keithley 195A DMM Option 1950
https://github.com/openscopeproject/keithley1950

ac-dc dmm keithley195a kicad option pcb trms

Last synced: 27 days ago
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Keithley 195A DMM Option 1950

• Host: GitHub
• URL: https://github.com/openscopeproject/keithley1950
• Owner: openscopeproject
• License: other
• Created: 2020-01-19T04:43:48.000Z (over 5 years ago)
• Default Branch: master
• Last Pushed: 2020-01-19T04:44:27.000Z (over 5 years ago)
• Last Synced: 2025-07-23T06:44:21.033Z (3 months ago)
• Topics: ac-dc, dmm, keithley195a, kicad, option, pcb, trms
• Language: HTML
• Size: 1.25 MB
• Stars: 9
• Watchers: 7
• Forks: 3
• Open Issues: 0
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

          
# Keithley 195A DMM Option 1950

Keithley Instruments 195A Digital Multimeter is a 5½ digit resolution 200 000

count instrument that was manufactured in the 80's, possibly early 90's. It was

available in two configurations: base model that only had DC Volts and Ohms

measurements and model with 1950 option, which added DC/AC Amps and AC TRMS

Volts measurements.

Keithley DMM line has long replaced 195/196/199 series with newer models but

these still show up on Ebay and other outlets and they offer great performance

for reasonable prices. Unfortunately most of the 195A models available online

are the ones without 1950 Option.

This project aims to recreate the 1950 Option PCB and circuitry using modern

components.

In the process some upgrades and some compromises were made. For example this

version of 1950 option board is based on AD8436 trms chip that along with newer

opamps provides higher bandwidth and better overall specs than much older AD536

of the original. On the other hand cheaper shunt resistors are used (because

of their availability) with worse drift and tempco characteristics.

**High voltage** operation using the new board is also **NOT** recommended or

tested.

---

## BOM

See [bom](https://openscopeproject.org/InteractiveHtmlBomDemo/html/Keithley1950.html)

for this board generated by

[InteractiveHtmlBom](https://github.com/openscopeproject/InteractiveHtmlBom)

plugin for KiCad.

## Schematic

![img](https://i.imgur.com/aX9WxCY.png)

## 3D render

![img](https://i.imgur.com/0c3jkUk.png)

## Pictures

End result installed in the meter

![img](https://i.imgur.com/UacUyqy.jpg)

Original board next to new version

![img](https://i.imgur.com/7FVghgY.jpg)

Close up of rev A board with Genuine Bodge™ visible on the left

![img](https://i.imgur.com/l0e0v63.jpg)