User manual

Table Of Contents

USB DrDAQ User's Guide 21

Making accurate measurements

The DD101 will give good readings of humidity and show trends well. However, if you

need to make more accurate measurements, you will have to calibrate the sensor.

The calibrated sensor could have an accuracy as good as ± 5% though this depends

on how well the calibration procedure is carried out.

The output of the sensor may vary over time. For this reason you should calibrate the

sensor regularly (at least once a year).

Basis of the calibration method

Calibration relies on the general physical properties of saturated solutions. The

humidity above such solutions in closed containers is known quite accurately and is

used to calibrate the sensors. Chemical salts used for this purpose include potassium

chloride, magnesium chloride and magnesium nitrate.

Note: The humidity that exists above all such solutions varies with temperature.

The standard solutions may be harmful to your skin, eyes or when

swallowed. Take all necessary precautions to avoid contact when

preparing and using the standard solutions.

Note: For the highest accuracy you should compare the readings from you DD101 with

the readings from a calibrated 'laboratory standard' reference humidity gauge.

Calibration of the sensor involves:

Preparation of the calibration equipment.

Measurement of the standard saturated solutions.

Creation of calibration data for the USB DrDAQ software.

A check that the calibrated sensor is accurate.

Note: You must measure at least two different standard solutions to provide two or

more fixed points for calibration.

Equipment you will need:

USB DrDAQ with DD101 sensor

Pico DD100 Temperature Sensor

At least two Standard Solutions

A label for the DD101

A test container

An insulated box

A stand for the DD101

[Optional] high-accuracy, calibrated reference 'laboratory standard' humidity gauge

Stand

It is very important that the standard solution does not enter the case of the DD101.

The solution may damage the electrical components of the sensor. Therefore the

DD101 needs to be suspended in the test container clear of the standard solution. A

small stand is the best way to hold the sensor above the solution. The stand may be

any object (open framework) that is impervious to the standard solution. Make sure

that the material that your stand is made from is compatible with the test solutions

you intend to use.