Calibration, 1. before calibration – Yokogawa ISC450 4-Wire Analyzer for Inductive Conductivity User Manual

Page 44

IM 12D06D05-01E

6. CALIBRATION

6-1. Before calibration

1. When is calibration necessary?

Calibration of con duc tiv i ty in stru ments is not

nor mal ly nec es sary as the con duc tiv i ty cells

are man u fac tured to close tol er anc es and do

not al ter in use.

If the cell has severe fouling or been sub ject to

abrasion (possibly during cleaning) it may be

necessary to calibrate.

Since the ISC450G/ISC40 inductive con duc-

tiv i ty system measures the conductivity of the

“liq uid winding” through the doughnut, part of

this “measuring cell” is outside the dough nut.

If there is little space between dough nut and

process piping, calibration with a sam ple of the

process fluid is necessary to en sure ac cu rate

measurement.

2. How is calibration done?

Calibration is carried out by measuring a

so lu tion which has known conductivity and

ad just ing the instrument to show the cor rect

conductivity value.

The calibration can be achieved using one of

two methods:

1) A calibration solution can be prepared in

the laboratory. A salt solution is prepared

with a known precise concentration.

Thetem per a ture is stabilized to the ref-

er ence tem per a ture of the instrument

(usu al ly 25 °C). The actual conductivity

value of the solution is taken from tables.

To calibrate the in stru ment, the sensor is

removed and sus pend ed in the solution,

the conductivity val ue from the tables is

then entered and the cal i bra tion routine

completed.

Make sure the sensor does not touch the

sides of the container, refer to Figure 6-1.

2) Alternatively the instrument can be cal i brat-

ed using the process solution meas ured

with a standard instrument. Care must be

taken to make the measurement at the

ref er ence tem per a ture since differences in

the type of tem per a ture compensation of

the instruments may cause an error.With

this method the sensor is not removed

from the process. This method is the

most convenient method of calibrating

the ISC450G converter. Since the sensor

is im mersed in the process, errors

caused by in stal la tion characteristics are

compensated for.

Note! The standard instrument used as

ref er ence method must be ac curate.

Yokogawa recommends that the Model

SC72 personal conductivity meter be

used for this purpose.

X = MIN 25 mm

igure 6-1.

Sensor in calibration solution