OHAUS ST20D Instruction Manual

ST 20D Pen DO Meter

                                  Instruction Manual

Welcome to OHAUS (www.ohaus.com)!

After more than a century of perfecting the art of measurement through our durable weighing products, OHAUS 

precision is now available in a line of portable electrochemistry products that provides accurate measurement of DO, 

pH, ORP, conductivity, TDS and salinity.

ST series pen meters are the economical option when you are simply looking for meters that are easy to use and 

provide accurate measurements.

The pen meters should not be used by Children of age 12 or younger.  

This product conforms to the EMC Directive 2004/108/EC.  The Declaration of Conformity is available online at 

europe.ohaus.com/europe/en/home/support/compliance.aspx.

Thank you for choosing OHAUS waterproof pen Dissolved Oxygen meter ST20D. Please read the manual completely before 

use.

First Usage

Turn off the membrane part, fill the electrolyte, then turn on the membrane. Warm up the DO pen meter by turn on it. The meter will turn off 

automatically after 10 minutes.

Calibration and measurement

After warm up, turn on the meter. Put ST20D in the air, press button “Cal”;

The meter will display “100” and blink under the signal, now the meter is calibrating 100% DO value; after 3 to 5 minutes when the signal is stable, 

press button “Hold/Enter” to finish 100% DO calibration.

Now we have two options:

1. Press button “Hold/Enter” to finish 1 point calibration and exit to measurement interface.

Note: Ohaus suggest that only do one point (100%) calibration for ST20D. Do not need perform 2 point (0%) calibration 

if the sample DO value is not too low (e.g. <1 mg/L).

2. Put the ST20D into the Zero-Oxygen solution. Press button “Cal” to do the 0% point calibration, LCD will display and blink “0” under the signal, 

after about 3 minutes when the signal is stable, press button “Hold/Enter” to finish 0% calibration.

Zero-Oxygen solution is saturated Na2SO3

(CAS NO 7757-83-7) solution. Ohaus offer DO zero-oxygen chemical (30059257).

After calibration, rinse the pen DO tip, then we can measure the sample.

Maintenance and Storage

After the usage, turn off the membrane, rinse the electrode and membrane, makes them dry and turn on the membrane part to store.

Harsh samples may short the pen meter life time, such as sticky, dirty or oily liquids.

The electrode is replaceable.