Technical information

ICT in the science department 1634 © CLEAPSS 2005
16.10.1 Dataloggers and their software
A datalogger is normally a small interface (or box) with sockets allowing one or more
plug-in sensors (see section 16.10.2) to be connected. A lead normally connects the
interface to a computer on which appropriate datalogging software is installed.
A datalogger converts signals from one or more sensors into a form suitable for the
computer. A datalogger often includes memory to store readings from sensors without
a computer present (remote logging).
The electrical power supply for a datalogger may be directly from the host computer,
via a mains transformer, a rechargeable battery or a disposable battery.
The operation of the datalogger is controlled by software. Each datalogger system
usually has its own software but it may also be possible to use third-party software
such as Insight from Logotron.
A starting package often includes an interface, basic software and simple sensors (eg,
temperature, light and pH).
16.10.2 Sensors for dataloggers
A wide range of sensors is available to monitor and measure various parameters, as
indicated by the list below. Schools should always check that the range of sensors that
are available for a particular datalogger system suits their current and future needs,
before deciding which model of datalogger to purchase.
Types of sensor
Acceleration; Barometer; Carbon dioxide; Charge; Colorimeter; Conductivity; Cur-
rent; Dissolved oxygen; Drop counter; ECG, Flow rate; Force; Heart rate; Infra-red
radiation; Ionising radiation; Light; Magnetic field; Motion; Oxygen; pH; Photo/
Light gate; Position; Pressure; Relative humidity; Respiration; Rotary motion;
Sound; Temperature; Timing; Ultra-violet radiation; Voltage.
Particular points for selected sensors
Conductivity
The conductivity of solutions is an important parameter in modern chemical
instrumentation and may be used to follow the progress of a reaction. A typical
investigation would be to record conductivity and pH as they vary in a suitable
titration reaction or a rate of reaction experiment.
Conductivity sensors are relatively straightforward to use; see section 17.3.2
(Conductivity) for further details.
Current
A current sensor is useful in many physics investigations. One example would be
to plot magnetic field (measured with a Hall-effect sensor) against current in a
coil.
Distance
Ultrasonic distance measurement is used by many automatic cameras to set the
focusing. The sensor used has proved to be very useful for teaching dynamics and
versions are now available from several suppliers. (See Velocity below and section
12.4.2, Timing methods.)
Ionising radiation
Radioactive decay curves (eg, of protactinium) are ideal examples for computer
display and data manipulation. A ratemeter sensor will convert a random train of
pulses into a voltage proportional to the pulse rate averaged over a period which
allows count rates to be studied over time.
Light
Light levels of interest in environmental studies can vary enormously, at least by
a factor of 100 000 to 1. Sensors, therefore, tend to have a logarithmic response
with the result that equal increments in output correspond to an increase of light
level by a certain factor; eg, a probe could increase its output by 0.2 V for every 10-
fold increase in light level. Usually exact calibration is unimportant and such a
response caters for the wide changes in light level that occur naturally.