KX Reference

[grizewald]

Thanks for the great advice Dr. Frank and TiN.

I wish I had a basement, but that's just a dream for us apartment dwellers.

I would not even dream of powering the references with a switched mode PSU! They are powered from my Thurlby PL320 linear supply:



I think I have a suitable metal tin to create a shielded environment for the reference and I should also be able to fit some LiPo battery packs in there to provide power for it. That will go a long way towards removing RFI influences. I just need to get some more screened PTFE cable as I seem to have run out.

I let the log continue running and got one huge -80ppm jump last night as shown in the plot below:



When that happened, I took my wireless environmental monitor and relocated it to the other side of the room. This forced me to restart my logging script as the subtask which adds the data from the sensor stopped updating when I had to unplug the sensor to move it. It is interesting to see what happened to the 34401A's readings after I restarted the script. If you look at the plot just after the -80ppm spike, there's a change in the logged voltage back to the 0ppm difference level when I restarted the script (which starts with a *RST command).

It looks like there was something causing an offset to the readings which got cleared when I reset the meter. By default, the 34401A should be performing an auto zero on every reading with the settings I am using, so either that's not true (and I will change the script to turn on auto zero explicitly), or there's some other offset source accumulating in the meter which isn't accounted for by the auto zero.

I hope it is caused by auto zero not being on by default. If it's not, and there's some other kind of offset building up over time, it kind of shakes my confidence in the 34401A for long term logging.

[beanflying]

I am about to populate a couple of these boards to add to the fleet. What is the best current thoughts on enclosures? I have a small stash of these metalised ones or should I stick to a full Aluminium one? Also still foam support or make some 3D printed supports around the perimeter of the board?

TIA 

[Andreas]

Hello,

I personally prefer massive metal cases: how do you want to connect a "guard" to your metallisation.
Usually a metallisation is at best a electrostatic shield (for DC) or very high frequencies in the 10 GHz range.

A real shield should have a minimum thickness of 0.5 mm.
Of course you are free to put a Teko steel enclosure (tuner box) within the plastic cabinet.

https://www.reichelt.de/index.html?ACTION=446&LA=0&nbc=1&q=teko%20steel

with best regards

Andreas

[BU508A]

Hello,

seems this link to Reichelt doesn't produce any results.

This one might work.
Click on the left side for "Steel sheet housing"

[hwj-d]

As Andreas sayd, effective shielding is a must. The Teko's 373.16 are tinned steel, but the binding posts likely to become a little wobbly. So best for me are the Hammond 1590 aluminium alloy or the HM971-ND. Some pictures because of the space requireds.

[grizewald]

It looks like there was something causing an offset to the readings which got cleared when I reset the meter. By default, the 34401A should be performing an auto zero on every reading with the settings I am using, so either that's not true (and I will change the script to turn on auto zero explicitly), or there's some other offset source accumulating in the meter which isn't accounted for by the auto zero.

I hope it is caused by auto zero not being on by default. If it's not, and there's some other kind of offset building up over time, it kind of shakes my confidence in the 34401A for long term logging.

I'll quote myself just in case anyone else runs into this.

When setting up the 34401A for logging on 10V DC, maximum resolution and NPLC 100, you could be forgiven for thinking that auto zero would be on by default. The 34401A user manual says that auto zero is enabled for CONF and MEAS when NPLC >= 1.



So I used the following commands to configure my meter:

*RST
*CLS
CONF:VOLT:DC 10, MAX
VOLT:DC:NPLC 100
INP:IMP:AUTO ON

The problem is, that contrary to what the manual tells you, auto zero is NOT on by default with these settings! So, if you think what you are measuring seems to be drifting more than expected, add the line below to your list of commands and auto zero will finally be on. (I added it after the last line in the list above.)

ZERO:AUTO ON

You will know it has worked as the time between each reading will be four seconds instead of two.