g disc drive ram non volatile memory etc that can temporarily or permanently store sensor data each of the environmental sensors 14 is connected to one of the external connectors 34 of the central unit 10 via a sensor module 12 as shown in fig3 each sensor module 12 includes a sensor port 36 an identification id circuit 38 and a module port 40 sensors 14 can be any conventional sensor device that measures an environmental parameter such as air flow humidity differential pressure temperature airborne particle count etc each such sensor 14 includes its own standard sensor cable 42 and terminal connector 44 thereon that connects to a compatible sensor port 36 different sensors 14 may have different types of terminal connectors 44 and thus the sensor module associated therewith must have a sensor port 36 that is compatible with that terminal connector a module cable 46 connects between the module 12 and central unit 10 with a first terminal connector 48 at one end that connects with module port 40 and a second terminal connector 50 that connects with one of the external connectors 34 as explained further below module cable 46 transmits power to the sensor 12 and sensor module 14 and transmits id information and sensor data to the central unit 10 calibration ports 41 can be included in sensor module 12 for those sensors that can be or need to be calibrated remotely where a calibration signal.