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Aquameter
™
Series Instruction Manual
10401-00188 Rev M
14. DO/EC Electrode Calibration and Maintenance
14.1. Recognising the DO/EC Electrode
The DO/EC electrode is easy to recognise
because it has a screw-on cap and four
stainless-steel EC sensor contacts on the
side (see photograph). Dissolved Oxygen
(DO) is measured at the end of the electrode
by the components behind the removable
cap. Electrical Conductivity (EC) is
measured on the side of the electrode by the
four stainless steel contacts.
14.2. DO Measurement Techniques
Aquaprobe models AP-300, AP-500, AP-
600, AP-700 & AP-800 utilise a Galvanic DO
sensor. This consists of an electrolyte filled
DO sensor cap with a clear, gas-permeable membrane stretched across a silver electrode.
Aquaprobe models AP-900 & AP-1000 utilise an optical DO sensor. This sensor does not
use a liquid electrolyte and has a black rubber gas-permeable membrane. See
The Tech Behind Aquaread’s Optical DO Measurement System
14.3. Precautions During Use
In order to achieve accurate Dissolved Oxygen readings with the Galvanic DO sensor, the
Probe needs to be either placed in flowing water, or needs to be stirred or raised and
lowered continuously to ensure a constant flow of fresh water over the DO Electrode.
If
there is no water flow across the Probe, the oxygen in the immediate area of the DO
Electrode will be consumed and the reading will start to fall.
Aquaprobe models AP-900 & AP-1000 featuring the Optical DO sensor do not suffer from
this restriction. No water flow is necessary when using these probes.
EC measurement is not possible with the lower Probe sleeve removed as the sleeve
forms an integral part of the measurement system
.
Never immerse the Probe without the DO Cap fitted or with a damaged membrane. If
the components at the end of the DO/EC electrode come into contact with the liquid
being tested, serious damage can occur to both the DO/EC electrode circuitry and
the pH/ORP electrode.
14.4. Calibrating the DO/EC Electrode
Calibration of the EC section of the electrode is normally carried out during RapidCal (see
). EC can be calibrated separately using different EC
Calibration Standards, this is covered after the DO calibration section (
The DO section of the electrode should be calibrated at the Zero saturation point at least
once a month. Before each day’s use, the 100% saturation point should be checked in
moist air and re-calibrated if necessary. For optimum
accuracy, calibrate the DO100% point
as near to your sample temperature as possible (within the calibration temperature limits of
5
°
C - 40
°
C).
© 2011 Aquaread Ltd.
www.aquaread.co.uk
Page 32 of 64