All the right signals? | Archive Titles

Table 1: Gas sensors (from table 3.7 in CIBSE Guide H)
Sensor	Element	Description	Types	Advantages	Disadvantages	Applications
CO₂ sensor	NDIR optical cell (non-dispersive infra-red)	Measures the absorption of infra-red radiation by Co₂ in air	Wall-mounted housing with CO₂ permeable membrane for DCV applications	Small size, insensitive to humidity or other vapours	Cost	Demand – controlled ventilation for occupied spaces
Multi-gas sensor	Tin oxide film	Detects oxidation on a heated tin dioxide surface. Sensitive to heavy odours, smoke and solvent gases	Various wall and duct housings	Sensitive to wide range of contaminants	Relative rather than absolute measure of contamination	Multi-contaminant situations. Carbon dioxide control preferred for occupied spaces
Specified pollutant	Non-dispersive infra-red	Uses IR absorption. Sensor is specific to pollutant	Available for several gases	High accuracy and stability	High cost	Car park ventilation control (carbon monoxide and nitrogen dioxide); swimming pools (chlorine); air pollution monitoring (sulphur dioxide)
Obscuration	Optical cell	Detects absorption of light beam by suspended particles		High accuracy and stability	High cost	Roadway and tunnel ventilation control

Table 2: Some Network Protocols (From Table 4.3 in CIBSE Guide H)
Protocol	Standard	Comment
Ethernet	ISO 8802-3	Data transmission up to 10 Mbits/s. The most common IT medium
ARCNET	ANSI 878.1	High performance LAN with data exchange up to 2.5 Mbits/s. Used widely in industrial applications
BACnet MS/TP		Master slave/Token passing serial communications using an EIA-485 signal. Provides adequate performance at reasonable cost
Point to point	EIA 232	Serial communications between two devices. Typically used for dial-up communications using modems
LonWorks		The Lon network is based on the proprietary Neuron chip and can be applied to a wide variety of physical media
Batibus	ISO JTC 1 SC25	Uses twisted pair at 4.8 kbit/s
TCP/IP		Transmission Control Protocol/Internet Protocol. It encompasses media access, packet transport, session communications etc. TCP/IP is supported by a large number of hardware and software vendors. Several Internet protocols deal with aspects of TCP/IP. The most important have been collected into a three-volume set, the DDN Protocol Handbook
European Installation Bus		Uses twisted pair at 9.6 kbits/s