Sensors transmit back to cental monitoring station

Edited by the Engineeringtalk editorial team May 1, 2000

Monitherm's MLS2000 distributed sensing system uses standard sensors with small attached radio transmitters which link back to a central monitoring station.

For installations requiring dozens of distributed environmental sensors, the installation itself is often the most expensive part of the system - sometimes prohibitively so.

Now a new UK-designed system looks set to change that.

Monitherm's MLS2000 uses standard sensors with small attached radio transmitters which link back to a central monitoring station.

With no cabling and trunking required, costs are slashed.

Indeed, it is often true that any installation is disallowed on the grounds of unacceptable disruption, meaning that the development of a laboratory or production environment is held back.

Another drawback with conventional hard-wired data logging equipment is that there is a relatively low limit to the number of sensors that can be connected.

If wireless systems are used, to avoid the disruption caused during installation, the number of sensors tends to be restricted even further.

However, the MLS 2000 takes advantage of the recently relaxed legislation covering radio transmitters.

Using a licence-free 10mW signal on the 433MHz frequency, the system can transmit over a range of, typically, 250m with no loss of data.

Up to 128 sensor units can be used with each base station, with the range of sensors currently covering the measurement of temperature, relative humidity, carbon dioxide, oxygen and light levels.

The data is logged on a hard disc, from which it can be output to floppy discs or CDs.

Because the system has been designed for critical installations, the base station is equipped with an uninterruptable power supply (UPS) so that it will function as normal for a full 24 hours in the event of a power failure.

The base station also has a facility for generating visual and audible alarms, as well as auto-dialling ten telephone numbers until it is acknowledged.

The upper and lower alarm limits can be set individually for each sensor, and a time delay can be incorporated to prevent false alarms occurring when, for example, a door is opened.

Data may be logged at time intervals ranging from two minutes to 24 hours, though the transmitters operate continuously, which means that the alarm is raised immediately if a limit is exceeded.

In terms of data integrity, the system is UKAS-certified and all measurements are fully traceable.

Tests undertaken at Addenbrookes Hospital, Cambridge, showed that the transmitters do not interfere with RFI-sensitive equipment.

The elimination of wiring and, consequently, the vastly reduced installation costs make the Monitherm system extremely attractive for new projects.

However, the way the system can be introduced with minimal disruption will make the system highly desirable for retrofitting to existing laboratories, clean-rooms or other similar environments.

The sensor probe is simply installed in the conventional way, and the radio transmitter - about the size of a mobile phone - sits in a holster that is fitted in a convenient position nearby.

The price for a base station is around £12,000 and each sensor and transmitter unit is about £200, though this depends on the characteristic being monitored because, for example, relative humidity and carbon monoxide sensors are more expensive.

The company estimates that systems with 50 or more sensors can be easily justified.