Abstract: A fluid flow controller (1) comprises a variable aperture flow control valve (5) having an inlet to receive fluid from a supply source and an outlet to deliver fluid along a conduit (6). Downstream of the valve (5) is a back-pressure regulator (8), which in turn delivers fluid to an outlet (9), whilst a permanently open orifice (11) is connected to the conduit (6) upstream of the regulator and provided with an exhaust outlet (12), the characteristics of the valve (5), regulator (8) and orifice (11) being so selected that upon a slight opening of the valve (5), the regulator (8) maintains a closed condition, while further opening of the valve (5) raises the fluid pressure at the regulator (8) which commences opening, to provide a continuous exhaust flow at the exhaust outlet (12), to extend the satisfactory operating range of the flow control valve (5) down to very low flow rates. The controller (1) is suitable for use with a sulphuric acid dewpoint monitor.

Abstract: A fail-safe shutter (13) for a “cross-stack” monitor, comprises a body member (14) having an aperture (1) through which, in use, an associated monitoring instrument is adapted to sight. A gate (3) is movable between a retracted, open position in which the aperture (1) is exposed, and a closed position in which the aperture (1) is closed-off by a portion of the gate (3), and means are provided to bias the gate (3) towards its closed position.

Abstract: A retro-reflector assembly (1) for incorporating in an opacity monitor, includes several small corner-cube prisms (2) of cylindrical section. The invention also includes an opacity monitor incorporating a retro-reflector assembly as defined above.

Abstract: A fluid flow controller (1) comprises a variable aperture flow control valve (5) having an inlet to receive fluid from a supply source and an outlet to deliver fluid along a conduit (6). Downstream of the valve (5) is a back-pressure regulator (8), which in turn delivers fluid to an outlet (9), whilst a permanently open orifice (11) is connected to the conduit (6) upstream of the regulator and provided with an exhaust outlet (12), the characteristics of the valve (5), regulator (8) and orifice (11) being so selected that upon a slight opening of the valve (5), the regulator (8) maintains a closed condition, while further opening of the valve (5) raises the fluid pressure at the regulator (8) which commences opening, to provide a continuous exhaust flow at the exhaust outlet (12), to extend the satisfactory operating range of the flow control valve (5) down to very low flow rates. The controller (1) is suitable for use with a sulphuric acid dewpoint monitor.

Abstract: A method of monitoring the temperature of a target (4), the method comprising:a) sensing radiation emitted by the target (4) at at least two different wavelengths;b) determining a temperature value from the sensed radiation in accordance with a first predetermined algorithm;c) repeating steps a) and b) a number of times to generate a set of temperature values;d) selecting a target temperature from the set of temperature values in accordance with a second predetermined algorithm; and,e) generating an output signal defining the target temperature obtained in step d).