JLS Designs Advanced Wireless Interfacing Units

The concept of this project developed in response to a need expressed to us by Draeger.
Adequate monitoring of atmosphere where toxic or asphyxiating gasses are used requires a
number of sensors linked to a central control and alarms unit. Frequently, the sensors are
linked to the control unit by a 2-wire interface supporting a 4mA to 20mA analogue signal;
the control unit resolves the measured currents into gas levels and initiates any alarm
procedures accordingly.
A key issue faced by companies developing and selling gas sensors is one of installation. The
control unit must often be located in an office or corridor some distance from the sensor(s), so
that extensive and intrusive cabling has to be installed. This represents a significant cost to the
end-user, as well as being a considerable disruption during installation.
The solution, which forms the basis for this project, is a set of bolt-on digital wireless
interfaces. A device will be realised capable of measuring the output current signal from a gas
sensor, and transmitting this information digitally through a wireless mesh network. A similar
device will be designed and built to collect the data from the wireless interfaces, and
reproduce the measured currents at the control unit. In this way, the control unit and sensors
need not be altered to accommodate the benefits that wireless technology brings; namely ease
and flexibility of deployment.
This novel solution is particularly advantageous for three reasons. The first is that the end-user
of the gas sensing system experiences significantly less cost and disruption when the system is
installed. The second advantage is that the wireless interfaces are agnostic as to their
application, so that they can be employed with equal success in a variety of different
applications. That is, the wireless interfaces perform no alarm or control of their own; they
simply capture and then mirror the output of a sensor at the control unit. This process could
easily be adopted, for example, with environmental monitoring using temperature/humidity
sensors, or corporate utility monitoring using water flow meters and electricity/gas meters.
The third key advantage is that, because of the principles of wireless mesh networks, it will be
possible to build additional monitoring devices into an application so that, for example, data
logging of the various gas levels can take place independently and without reference or
interruption to the control and alarms unit.
The focus of this project is the development of concept electronics and firmware which will
enable the wireless current measurement and replication. Each core component of the system
(i.e. current sensing, current sourcing and wireless interface) is already commercially
available in the form of chipsets which minimises project risk since individual parts are
proven. The challenge and novelty for the project is the bringing together of these components
into a reliable, cost-effective package.