DIGITAL pH METER (Update)

By Bill Reid.

My first experience using a digital pH meter was with the C.P. model as mentioned in the National Newsletter some while back. This particular model was kindly loaned by Rita & Major Pearle after a vist to their home in Colchester last Autumn.

The C.P. pH Meter is a most convenient sized gadget which could be clipped to your shirt or jacket pocket very much like a pen. It operates by four mini batteries which are easily replaced. I found Tandy dealers most convenient for this.

However, as my model was only on loan, this had to be returned when it was required, therefore I decided to buy one for myself. I Found that the C.P. model was no longer available and the day was saved by our Secretary, Ron Croad, giving me the address of Solex International and so wrote off an order for a meter.

As with many things these days, nothing ever seems to remain the same for long. I found that not only was the meter not C.P. but called "Champ" By Hanna (Instruments), even though it looked identical to the C.P.. but likewise Solex International had now become Analog & Numerical Devices Ltd, Unit 25. Swannington Road, Broughton Astley, Leicestershire, LE9 6PD.

However the one main diffence with the Champ model is that it is `self` calibrating, which I found very useful as I no longer used a pH `buffer` but simply dipped the meter into a small beaker of clean `cold` tap water, to reset it to around pH 7.

It has long been established that you must keep the pH sensor `bulb` damp and at around pH 7. However the instructions for the Hanna explain that it is alright to let the bulb dry out (a powder forms in the bulb), and all you need do is soak the meter (bulb) in a bath of pH 7 for around 30 minutes before using. However it still recommends filling the cap with water at appx. pH7 for storage. A piece of sponge in the `well` will retain mositure for long periods.

I found the pH meter most convenient to use and a most useful addition to my W&M equipment.

I also asked Analaog to let me know of any other pieces of equipment they may have that would interest CRC members and in return I received a most extensive (and hefty) full colour catalogue of their wares. Most are extremely technical and expensive equipmebnt aimed at large firms. However I found that along with digital pH meter they also have two other items in identical design that may interest you. One is a Temperature `tester`. This has a range of -15 to 170C with a resolution of 1C. While you dip it into your water bath just like the pH meter, it also comes with an extension `probe` so that you can it with narrow necked bottles.

The other model is a Conductivity `tester` with a range of 10 - 1990 ppm and an accuracy of 0.2%. All use 4 mini batteries, but while the pH meter and temperature tester have a life of 1000 hours, the Conductivity tester only has 300 hours life. I think members would find the pH meter and Temperature Testers most useful. However just to confuse the issue of these meters looking identical whatever the name, the meters advertised in the catalogue are named "OMEGA". It is obvious that these meters are most likely made by the same people, but the selling name depends on the country they are marketed in. The Catalogue is obviously American as all prices are given in Dollars.

Another type of thermometer that you may find useful is the Thin Stem Pocket Thermometer. These are stainless steel with a large easily read dial. You can have a Farenhieght or Centagrade model, but there is also a dual dial model. As they need no batteries and easily clip onto the sides of your water bath, they can be left just about anywhere and include a stainless steel carrying case. They are very accurate and rugged with fast response from a sensitive bi-metal element with an accuracy of 1% of dial scale. I would suggest a dial scale of 0 - 200F would be idial for our use.

If you are interested why not drop a line to Analog for the latest prices. I would like to thank Analaog & Numeric for sending the very large catalogue and a very personal service.

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