pH meter batteries

[Mick Fagan]

Recently my pH meter, which is a “pHep® 3” pocket sized microprocessor pH meter, a Hanna Instruments company product, needed new batteries.

Normally this wouldn’t be a problem, except the specified batteries are 4 x 1.4 V alkaline batteries, which appear to be not available in this country any more. Or at least I couldn't find them when I looked around.

Thinking laterally, I reasoned that batteries would over the course of time drop; therefore the meter has the ability to operate over a range of voltage. In fact, the unit tells me when the batteries are too low to work and need replacing.

The closest voltage I could get is 1.5 V so I loaded them in and then proceeded to calibrate in an initial buffer solution of pH 7 as per normal. Calibrating to an alkaline buffer solution of pH 10, I checked my freshly mixed C41 developer solution. After years of mixing this solution up, I know pretty much exactly what the initial pH of this solution comes out at, before I adjust for final pH.

The reading was within 0.1 pH of what I would expect, I was pleased.

Whilst this was satisfactory and the subsequent film I developed, appears to be alright, I wonder if anyone can give me an idea of just how much significance the battery voltage can be, or is, with this kind of instrument?

The supplier of the product in this country wasn’t too sure whether or not the voltage difference would be a problem, not really a great help.

When I print the negs, I will have a much clearer idea of anything awry!

Mick.

 

[Sparky]

I'm sure it totally depends of the design of THAT specific instrument. I'm sure, perhaps not unlike, say, light meters, that some pH meters are more tolerant of voltage fluctuations than others. It's all in the wiring.

 

[Steve Smith]

The circuit for this meter will include a voltage reference and/or regulator with which to reference its readings to. Otherwise its accuracy would vary as the batteries aged.

I would be fairly certain that using 1.5v cells instead of 1.4v would cause no problems at all.

As Sparky says, some lightmeter though do not have this feature and are more intolerant to battery voltage fluctuations.


Steve.

 

[Mick Fagan]

Many thanks for the replies, I think the unit should perform reasonably accurately as well, I just wasn't too sure as I know very little when it comes to meters and their respective foibles.

The unit does have an automatic temperature adjusting feature built in and is the third one of these meters I have had in about 14 years. The first one was a very basic model, one had to get the solution to 20 C to get an accurate reading, bit of pain and a time waster.

The second unit was kitted out with an automatic temperature adjusting thing as well, but I dropped it into 1 litre of C41 dev.

The current one is as the second, but is fully waterproof to the point of total immersion. As a result of having this wonderful feature, I haven't managed to drop it into any solution, yet!

Mick.

 

[Mike Wilde]

Yes, microprocessor equals regulated power

The digiatl chip set will need a stable power source for its own purposes, and the reference cell will alos be regulated, as other posters have mentioned.

Most electrical stuff is more forgiving that you might think. I charge my Metz60 ct-1 power pack with 6.43V ac effective volts, that once powered a Brother adding machine. It was rated at 7v, but when loaded it drops to the level noted. The flash still fires plenty long enough between charges, and I got the flash going after buying it at a garage sale for $20, and putting a new dryfit battery in it for $0.

 

[Photo Engineer]

I have the Hana waterproof meter that takes the 4 button batteries you describe. I can buy direct replacements here at Radio Shack.

PE

 

[Mick Fagan]

Mike, interesting information there.

PE, do you have a model number or manufacturers part number, for your batteries?

I don't believe we have radio shack here. If I was able to get a part number or battery model number, I may be able to cross reference it with something that can be locally sourced.

Mick.

 

[Kevin Caulfield]

Mick, our Tandy used to be a pretty close copy of Radio Shack, so they may be able to help.

 

[Mick Fagan]

Kevin, I tried Tandy, but Tandy Australia holds quite a few different lines to their US counterpart.

They did have various 1.4 V batteries, but of the wrong size. :rolleyes:

Mick.

 

[ath]

The key word here is "alkaline". Alkaline single cells start out with a voltage slightly above 1.6 Volts when really fresh and drop during their lifetime below 1 Volt. Normally they are reffered to as 1.5 Volt cells.
This voltage change over lifetime leads to the conclusion, that electronics designed for alkaline batteries has to be either per se insensitive to this change or includes some kind of stabilization. In case of electronic meters one can be quite sure, that there is some kind of stabilization inside.

 

[Photo Engineer]

This may be a change, but in the instructions my meter specifies the 357 battery.

Radio Shack has a 357 or LR44 which is a 1.5V Silver Oxide.

The battery packet says that it also replaces the alkaline batteries of the same dimension.

PE

 

[Mick Fagan]

Andreas and PE, many thanks for the input.

It would appear that there has been a change regarding the battery type (or voltage) being recommended. My latest pH meter was one of the first of it's type in this country, that and the everchanging worldwide battery supply situation, could be a reason for the difference.

I think I'll be content to continue with the current situation.

This forum really is a great wealth of information.

Mick.