The T3576 is a multifunctional digital Zig 2.4 GHz Wireless Mesh Network sensor comprising three sensors (sound, volatile organic substances (VOCs) and ambient temperature) in one package.
- SOUND – SOUND PRESSURE LEVEL (“DB SPL”)
Sound level is measured with a low power MEMS microphone and low power op-amp amplifier section. The principle is to measure the peak signal amplitude and approximate an RMS signal level measurement which can then be related to loudness in dB SPL. The microphone signal is amplified and peak detected before sampling by the ADC. Two separate gain stages allow wider dynamic range to cover from 30 dB to 120 dB. The analogue circuit requires 200mS to stabilise and measure an audio signal.
- VOLATILE ORGANIC SUBSTANCES (“VOC’s”)
The VOC sensor reacts to a number of organic carbon based chemical compounds. The T3576 is sensitive to 5 gases, Methane, Isobutane, Carbon Monoxide, Hydrogen and Ethanol.
The device offers high sensitivity to VOC’s with low power associated with a MEMS device. It uses a regulated 1.8 volts for the sensor heater which needs to run continuously.
It has an initial warm up period of 10 minutes during which no readings are created. The heater consumes about 8mA of current making the sensor power demand too high for battery operation. However, this is considerably less than non MEMS sensors which typically require 50 mA at 5v. The sensor’s microprocessor turns on the sensor element and is timed not to exceed its maximum of 2mS measurement per 1 second period. A watchdog is used to ensure these limits are not exceeded. The VOC sensor is designed to measure air quality and will detect such pollutants as cigarette smoke.
It is important to understand that this type of VOC sensor is not able to tell which of the above gases is in excess without knowing which gas is in the environment at the time of measurement.
The T3576 returns a ratio of fresh air against a measured value. This ratio is saved as a percentage where 100% is the value that should be returned in fresh air. For example, if the value returned was 50%, then we can say that if the gas in excess was Isobutane, the gas concentration would be 20ppm. Whilst for the same percentage, if the gas in excess was
Ethanol, it would be 2ppm.
- AMBIENT TEMPERATURE
An on-board thermistor is used for ambient temperature measurement. Here, temperature readings are taken every 6 seconds to produce an average reading for every minute.
- Power – mains plug type 12VDC power supply.
- Includes a built-in Zig 2.4 GHz Wireless Mesh Network range extender