| Products > Test Equipment |
| Some old school instruments showing how it's done (HP 3325A and Fluke 8506a) |
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| SilverSolder:
All mine have GPIB, I've never seen the serial option. You've got a rare one! :D |
| SilverSolder:
--- Quote from: dietert1 on January 25, 2021, 06:54:58 am ---Used our two old Fluke 8502A recently. One of them shifts 15 ppm in 10 V DC range when connecting Guard to Low, the other one doesn't. Any ideas? [...] --- End quote --- One of mine had a problem where Guard was shorted to Ground, due to a too-long chassis screw touching the bottom of the PCB. It exhibited similar odd behaviour. I had another weird problem, where the 10V range would shift by 10ppm when turning on the Filter. I'm pretty sure it is a leaky FET in the switching arrangement, but it made me think that since these things use JFETs as switches all over the place, any one of them could probably cause weird and subtle problems.... (I fixed mine by swapping the Filter module with a known good one). The nice thing about these meters is that it is so easy to swap modules. Since you have two meters, you can try swapping modules until you see which one is causing the problem? |
| joeqsmith:
New 2ppm parts installed and finished the alignment. Showing the Caddock TK series 10ppm 1.9Meg. It's about 10 counts lower from the 34401A but good enough. Checked out the serial board. Glad I did. That thing has jumpers that are just wires press fit in place. I'm surprised that they never fell out. I set it up for 9600 8N1 and stuck a null modem and my old RS-232 jumper board (a relic from the 80s). Fired right up. Shown tracking a 40ohm 0.005% 1ppm part. Top cover still isn't installed but with the clam shells, I doubt it will make much difference with the drift. I used some long lead to zero it and plugged the resistor directly into the unit. 2W mode. Not surprised it's reading a bit low. The manual talks about sending a 0 to enable the average and O0 to disable it. I can't seem to get that to work but the rest of the commands seem fine. I'll let it collect some data over the day and see how it behaves. |
| SilverSolder:
I love your "draft excluder" box - what is it? Looks highly scientific! :D Which parts did you replace? I've been thinking of swapping some of the op amps... there are modern ones that are orders of magnitude better. I have never actually tried setting the zero over GPIB - in the middle of tidying up the work area, slow going... I'll have a go at it when I've set it all back up. |
| joeqsmith:
--- Quote from: SilverSolder on January 25, 2021, 07:48:14 pm ---I love your "draft excluder" box - what is it? Looks highly scientific! :D Which parts did you replace? I've been thinking of swapping some of the op amps... there are modern ones that are orders of magnitude better. I have never actually tried setting the zero over GPIB - in the middle of tidying up the work area, slow going... I'll have a go at it when I've set it all back up. --- End quote --- The black box on top is just an old RS232 tester. There's no standard so these were common back in the day to sort out how to wire the cables. I have now fitted the correct connector and wiring so the meter just plugs directly into the PC. Some parts were out of spec enough where it could not be adjusted. These were replaced with higher quality parts. Where my manual show 0 as the commend to set the average and O0 to disable it, other manuals show it as O to enable the average. Explains why the command didn't work. Showing the drift over five hours with the 40ohm part. I then reinstalled the 1.9M as I had collected data from several meters using this part. |
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