User Guide

- 11 -

6 PH CALIBRATION

IMPORTANT: When Calibration mode is entered, controller automatically goes into

a “HOLD” mode where the 4-20 mA output freezes and relays are de-activated (if it

was in an activated condition). Upon return to measurement mode, both 4-20mA

output and relay activities resume, depending on settings.

The αlpha pH 190 controller features seven preset buffer values (pH 1.68, 4.01,

6.86, 7.00, 9.18, 10.01, 12.45) for quick auto-calibration at one or two points. The

first calibration point must be pH 6.86 or 7.00. When you calibrate this

instrument, you need to use FRESH standard pH buffer solution that matches

these values.

NOTE: If you are in ORP mode, see Program 3.0 for instructions on switching to

pH mode.

1. Press CAL / ENTER key to directly access the Calibration mode when the unit

is in pH measurement mode.

NOTE: Instead of pressing the CAL/ENTER key, you can also enter the Calibration

mode using the password code procedure as explained in Section 5.

2. The display scrolls BUFF and either pH 7.00 or 6.86. You must calibrate at

one of these two buffers for the first calibration. Use ▲ / ▼ keys to select pH 7.00

or 6.86.

3. Make sure the electrode is in the buffer solution. In ATC mode, you must also

immerse the temperature sensor in the buffer solution. In the symmetrically high-

resistance measurement mode, you must also immerse the solution ground

(potential equalization pin) in the buffer.

4. Allow the electrode time to stabilize.

5. Press ENTER. The instrument will blink with the un-calibrated pH value

corresponding to the mV output of your pH probe. If the value displayed differs

substantially from the buffer value, this indicates electrode drift. Consider replacing

your electrode.

6. Press ENTER to confirm the buffer value. The display blinks the calibrated

value twice, shows “DONE” and moves to the next buffer.

NOTE: Buffer must be within ±1.5 pH of the value you are calibrating to or Err1 will

be displayed flashing. To clear the Err1 display and return to calibration mode,

press ▲ / ▼ keys together.