ELCO LI 127 ph meter service manual or calibertion trick

[Rohith_elec]

I have a ELCO LI 127 ph meter, anyone know how to caliberate it ?

 

[BradtheRad]

Distilled water should read 7.0 (neutral).

There's also de-ionized water, which implies it is neutral.

An internet search turns up tables of readings of various acidic and alkaline substances.

https://www.elmhurst.edu/~chm/vchembook/184ph.html

 

[Rohith_elec]

The problem is i opened the instrument when it showed the wrong readings and tried to adjust the value with tht 7PH buffer in the internal preset pots, so now the value becomes steady at 7 even if the test liquid changes. i changed wrong presets, i suspect ...

 

[BradtheRad]

The pot adjustment was probably set at a threshold volt level. Was there any paint or glue on the pot? Can you examine it closely with a magnifier?

You'll have to go through some effort to restore any semblance of calibration.

First see if the manufacturer's website tells you anything about re-calibration. Call on the phone maybe. They may quote you certain volt readings that you should see at certain test points.

If you can't go that route...

Try dipping the probe in something acid that you can expect a certain pH (such as lemon juice).

Adjust the pots so you obtain a sensible reading.

Avoid turning the pots to either extreme, just in case it may admit overmuch current and they omitted safety resistors.

Make drawings of the pot positions as you go.

Watch for a point where the reading changes, in case it only occurs within a narrow window of adjustment.

See if dipping it in water brings it back to 7. Alternate as you need to.

Then do the same process with something alkaline (ammonia?).

Make drawings whenever you make progress.

 

[Rohith_elec]

ok, now i made it

But is it because of voltage fluctuation, the reading inside changes every time i switch on the Ph meter ?
or it because of some component faulty in the circuit ?

 

[BradtheRad]

Good work. Persistence pays off.

It is common for many instruments to show odd readings as circuitry powers up.

It should settle after a few seconds.

If the reading does not settle to zero then perhaps you must press a Reset button?

Do the instructions say the probe should be dipped in distilled water first, in order to establish zero pH?

 

[Rohith_elec]

problem is , i dont have the manual with me,

I dips the probe in pH 7 buffer at startup