10 August 2014

590. Home-made Titrino tip

Metrohm make a range of autotitrators called titrino, titrando etc. While they are great, they are expensive (ca AU$15,000 +/- 5,000) -- and the parts are ridiculously overpriced. For example, a simple pH electrode cable costs AU$100-150, which isn't a good use of taxpayer money.

I'm also not a big fan of their titration tips, one of which is shown in the photo below

The piece in this photo costs AU$30:
AU$30 -- reasonable?

Besides, in my own experience they don't work as well as the home made tips we used in a lab I used to work in.

So, here's a description of an alternative type of tip for doing titrations with a titrino.

The design in my old lab:

This is the tip -- it's a glass capillary which is connected to 1/16 PTFE tubing using a piece of elastic silicone tubing
The titrino is connected to the 1/16 PTFE tubing via an M6 (or 1/4-28) PTFE union.
The PTFE tubing is connected to the union using an 1/4-28 (or M6) ferrule
Like this

In my current lab:
Since I wasn't sure what the size of the capillary and the connecting silicone tubing was, I had to guess, and used the following parts:

Capillary OD 0.66 mm ID 0.5 mm
Silicone tubing OD  3 mm ID 0.5 mm
PTFE tubing 1/16 (ID 0.5 x OD 1.6 mm)
1/16 ID and 1/4 OD PEEK Ferrule
1/4-28 PTFE connector

It basically came down to what I could order online from a Chinese equivalent to ebay called taobao.

NOTE: the capillary here doesn't go that great with the silicone tubing, so I had to glue it using silicone glue. A smaller ID silicone tubing or a larger OD capillary might work better. Note also that you'd want as thin a capillary ID as possible though to avoid diffusion and leakage.

Here's the assembly (the glass capillary is a bit short since it broke):
And here's the capillary with the silicone part (the light in my office is pretty bad).
I used silicone glue to fix the capillary in place:
Some more photos of the different parts:
Very affordable Chinese capillaries -- $5 for 1,000!

1/16 inner and 1/4 outer diameter PEEK ferrule

The PEEK ferrule and the M6 (1/4-28) union

02 August 2014

589. Gnome-shell 3.12.2 -- another feature gone

The Gnome team has been removing feature after feature from different gnome-related applications. In the current version of gnome-shell (3.12.2-3) on debian testing (jessie) there's yet another feature gone -- you can't access the audio settings from the desktop.

Whether you use right- or left-click on the audio icon, you get the same menu. Clicking on the audio (left- or right-click) icon in that menu only causes the volume to go to zero.

Instead, the only way to access audio settings is now via the system settings which takes longer and involves more clicks. It's a minor nuisance if you're used to how gnome has previously worked.

29 July 2014

588. ata6: SRST failed (errno=-16) AND disk-by-uuid does not exist

The problem:
I've been having boot issues with one of my nodes. Everything is fine up to and past GRUB:

Then this happens:
[21.405411] ata6: SRST failed (errno=-16)

And typically I get dumped in a shell:
ALERT! /dev/disk/by-uuid/xxxx does not exist

Towards the solution:
blkid shows both disks:

Either way, turns out the way to get the system to boot is pretty simple. Type exit and hit enter.

exit leads to successful boot
Looking at dmesg this is what happened:
[ 1.998149] usb 2-1: Product: USB Optical Mouse [ 2.005374] input: USB Optical Mouse as /devices/pci0000:00/0000:00:12.1/usb2/2-1/2-1:1.0/input/input1 [ 2.005452] hid-generic 0003:0461:4D81.0002: input,hidraw1: USB HID v1.11 Mouse [USB Optical Mouse] on usb-0000:00:12.1-1/input0 [ 6.476845] ata6: link is slow to respond, please be patient (ready=0) [ 11.465026] ata6: device not ready (errno=-16), forcing hardreset [ 16.665379] ata6: link is slow to respond, please be patient (ready=0) [ 21.485411] ata6: SRST failed (errno=-16) [ 26.685767] ata6: link is slow to respond, please be patient (ready=0) [ 31.505806] ata6: SRST failed (errno=-16) [ 31.894576] uhci_hcd: USB Universal Host Controller Interface driver [ 36.706152] ata6: link is slow to respond, please be patient (ready=0) [ 66.579156] ata6: SRST failed (errno=-16) [ 71.611367] ata6: SRST failed (errno=-16) [ 71.623705] ata6: reset failed, giving up [ 105.133562] PM: Starting manual resume from disk [ 105.133565] PM: Hibernation image partition 8:2 present [ 105.133567] PM: Looking for hibernation image. [ 105.133775] PM: Image not found (code -22) [ 105.133777] PM: Hibernation image not present or could not be loaded. [ 105.189165] EXT4-fs (sda1): mounted filesystem with ordered data mode. Opts: (null) [ 107.565728] udevd[725]: starting version 175

Fixing it:
Increase the rootdelay so that the harddrive(s) have time to boot up. I think in my case the issue is that I found an ancient IDE drive which may be slow to spin up, and maybe even failing (I use it for /scratch).

Either way, edit /etc/default/grub and add rootdelay=90 (for example) to the end of GRUB_CMDLINE_LINUX_DEFAULT, e.g.
GRUB_CMDLINE_LINUX_DEFAULT="quiet splash vga=0x0318 text rootdelay=90"
Then do
sudo update-grub

and hopefully the next time your system will boot, although slowly.