Conference: World Meter Design Congress
Location: San Jose, CA, USA
Presenter: Mitsugu Terada
Abstract: Presented by Mitsugu Terada at World Meter Design Congress

A ZigBee sensor network for data acquisition and data monitoring is shown in this paper.  Sensor nodes are made for trial use in a laboratory class of undergraduate course in the university. 
The subject of the experiment is “Mechanical equivalent of heat” of physics laboratory.  Apparatus that are used in the experiment subject are a water calorimeter with electrical heater element and stirrer, a mercury thermometer, an electrical power supply, an ampere meter and a volt meter.  All operations are done by students manually and measurement data are recorded in their notebooks.  Distilled water contained in the copper container of the water calorimeter is heated by the electrical power supplied to the heater.  The water temperature is measured once per 30 seconds.  The value of the mechanical equivalent of heat is calculated from the values of voltage and current, and difference between the temperatures at start of and at end of the supplying electrical power to the heater.  So the sensors that measure values of current and voltage, and temperature are necessary for this application.

Some wrong operations are made by student in the experiment subjects.  It is worth for the instructors to have on-going experimental data in order for checking students’ operation.  An additional measurement system is required to monitor the students’ experimental process.  Owing to restricted space of existing laboratory facility and frequent arrangement change of experimental equipments, the ZigBee based data acquisition system is suitable for this solution.  Wireless network configuration and small size devices are highly preferable for additional measurement system.

A ZigBee network is configured by using commercially available device products.  A device is connected to a Microsoft Windows PC via USB interface.  The data that are collected by the remote nodes are sent to the PC that is set as a data sink.  Remote nodes are built of the ZigBee devices and sensors.  The current and voltage supplied to the heater are converted to DC voltage signals by converters.  The signal is inputted to two AD converter ports of one ZigBee device.  A thermocouple is connected to the cold junction compensator amplifier.  The signal from the amplifier is inputted to an AD converter port of the other ZigBee device.  The current, voltage and temperature data are transmitted according to the ZigBee protocol from the remote devices to data sink PC.  The data sampling rate is one sampling per second in this application.
The data are recorded in form of hexadecimal number by device control software and data file is stored in text format at the data sink PC.  Time dependent data change can be monitored by using macro function of spread sheet software.

Through some trial experiments, it is found that the considerable wrong operation is detected by monitoring experimental data.  It is expected that the additional measurement system is useful tool for instructors in university laboratory education.