Calibration, 1. calibration check with buffer solutions, 2. manual calibration mode – Yokogawa EXAxt PH450 4-Wire Analyzer for pH and ORP User Manual

Page 48: 3. automatic calibration mode

IM 12B07C05-01E

6-1. Calibration check with buffer solutions.

The following tips will help to produce a good

calibration.

1. Before starting a calibration, make sure the

electrode system is properly cleaned so that

the electrodes are fully functional. They must

then be rinsed with clean water to avoid con-

tamination of the calibration solution(s).

2. Always use fresh buffer solutions to avoid the

possibility of introducing errors from contami-

nated or old solutions. Buffers supplied as liq-

uids have a limited shelf life, especially alkaline

buffers, which absorb CO

from the air.

3. Yokogawa strongly recommends NIST

(primary) buffer standards in order to ensure

the best accuracy and best buffer capacity is

available. Commercially adjusted buffers (e.g.

7.00, 9.00 or 10.00 pH) are a compromise as

a standard, and are often supplied without the

temperature dependency curve. Their stability

will never be as good as NIST solutions.

Always ensure that the sensors are properly

conditioned, clean and filled with the correct

electrolyte solution (if appropriate) before starting

a calibration. Refer to section 7 (Maintenance),

and to the sensor instructions for details.

6-2. Manual calibration mode

The unit is adjusted to agree with the value of

a known solution. This may be a buffer solution

or a known process sample. The user deter-

mines the pH value, the temperature influence

and the stability.

1- A single point can be set to adjust only the

zero (asymmetry).

2- A second point can be set to determine the

slope (sensitivity).

6-3. Automatic calibration mode

The PH450G will provide prompts to aid the

user to make a good calibration. High quality

buffer solutions must be used for best results.

The user selects the buffer type that he is

using in the calibration menu. The buffer set is

selected in

Commissioning >> Measurement

setup >> Calibration setting>> Buffers