pH/CO2 controller set 7074/2 problem

[Grimson]

Hi, I have the 7074/2 set and I have a problem with the actual 7070/2 unit.

When trying to calibrate the pH 5/9 adjuster dial nothing happens on the display no matter how much I adjust the dial.
The pH 7 dial works as normal.

I have had the set a number of years as the original buffers expiration dates is in 2004 (I never throw anything away!).

Will I have to buy a new unit or do I have options to get it fixed?

Thanks for your help!

 

[rvitko]

ph 5/9 solutions have a fairly short life in storage, bacteria breakdown the solution over time, the expiration date on these is pretty firm, you may get an extra 6-9 months but not years. It may just be the solution, it may also be the controller or electrode. An electrode is essentially a weak battery, like any battery it dies, it puts out roughly 100mv, this varies a bit with pH, that is what the controller is interpreting to give a reading, after 2-3 years they are done and need to be replaced. Just picture the electrode as being like a cell of your car battery but instead of sulfuric acid, lead and lead oxide it is potassium chloride, platinum and platinum oxide, they just wear out over time. This is your second most likely culprit. The last most likely culprit is the controller, maybe some water damage is affecting the knob. The controller and electrode can be replaced seperately.

 

[Grimson]

Thanks Roger, I have bought new buffer solutions over the years for calibration but never replaced the electrode.
The last set of solutions expired last year so I will buy a another set, a new electrode and hope for the best!

Edit: Just looking at electrodes, other than material is there any difference between 7070.100 and 7070.110 ?

 

[rvitko]

You really can use any BNC electrode on the market. The 7070.110 is what we stock here, they are the most accurate, it is a glass tube that is refillable, like what you have now. 7070.100 is plastic, it is what most companies use, they aren't as accurate in general, but they are much less fragile. I don't stock those as you can pretty much get a plastic one anywhere.

 

[Grimson]

Thanks a lot for your help Roger!