Sensors in Domestic Automation Applications.
The demand for advanced electronics in domestic
automation applications has resulted in this market
becoming one of the world's fastest growing.
To address the significant opportunities arising,
Omron, one of the world leaders in control components
has developed a series of innovative new products.
A new pressure transducer for low pressure domestic gas applications
is the first of the exciting new roducts to be launched by Omron Electronics.
The installation of mains gas into school laboratories is just one example
of an application where the need for reliable safety measures to control
the flow of gas and to protect against gas taps being left open, is imperative.
D8M-08 micro pressure sensor
To address this problem an innovative electronic
pressure measuring system that centres on Omron's
D8M-D8 micro pressure sensor has been developed.
Originally developed in Japan for use as an emergency
cut-off for household gas supply in the event of an
earthquake, it eliminates switching problems associated
with mechanical pressure switches working at low pressures and also
provides enhanced reliability.
Traditionally, similar systems have used a mechanical pressure switch
on the appliance side of the solenoid to detect low pressure caused by
an open tap or other system leak. This type of switch, however, can be
adversely affected by hysterysis and as seasonal demands can vary
mains pressure, typically 28mBar, switching can become unreliable.
Failsafe start control system
The new apparatus provides a failsafe start control system for use
in school laboratories and kitchens, basically ensuring that all appliances
downstream from the solenoid isolation valve are off before the gas
supply is established.
As a result, the system uses modern electronic pressure transducers,
measuring the pressure differential between inlet and outlet supply. rather
than just supply pressure. This type of system is more reliable as it is
not subject to the effects of hystervsis and is able to take varying supply
pressures into consideration.
Simplistically, the device contains a variable capacitive cell, which
forms part of a CR oscillator. The capacitive cell has one fixed electrode
and one diaphragm electrode, which is acted upon by the pressure of
the gas supply. Any minute change in pressure bends the diaphragm
and produces a change in capacitance, which in turn produces a
proportional change in oscillation frequency. Therefore, any change
in gas pressure is proportional to output frequency.
One sensor is mounted either side of the solenoid shut-off, in line with
the gas supply. When the keyholder initially activates the system, the
inlet and outlet pressures are measured and compared. If outlet pressure
is greater than 80% of the inlet pressure, the solenoid valve is opened
and the gas supply can be used immediately.
If, however, the outlet pressure is less than 80% of the inlet pressure,
the valve is opened long enough to prove the outlet gas system and then
closed in order to take additional measurements. If the pressure differential
is then within limits after a pre-set time period, the valve opens permanently,
but if the differential is still too large, indicating an open gas tap or other
leak, the system is not activated.
The new pressure proving system ensures that the gas
supply is not established until all appliances downstream
from the solenoid isolation valve are off. In addition, the
system also guards against hazards associated with
supply pipe degradation, as the drop in pressure due
to escaping gas is discovered and the main supply is
shut off, making it ideal for commissioning engineers.
The sensors will also switch the gas supply off automatically if the gas
pressure drops dangerously low during use, guarding against an open
gas tap or system leak.
With a recommended operating voltage of 2.2 to 3.4V and a temperature
range of -10 to + 60ºC, the sensor produces an output frequency of
60 to 120 kHz, is suitable for use in indoor applications. Additional
safety features include a flange to bolt directly into housings where
push fit components do not provide the required level of safety and
a metal mounting plate for secure installation in critical applications.
From an article by Steven Heap, Product Manager, Omron Electronics
_____________________________________________________
For more information, please contact :-
Omron Electronics
Tel: +44(0) 20 8450 4646
Email: ukcc_sales@eu.omron.com
January 2001
