Sensing heads

Portable instrument should be of explosion-proof design fixed point systems may rely on remote sensing heads... 

Sensing heads should be located in draft-free areas where possible, as air flowing past the sensors normally increases drift of calibration, shortens head life, and decreases sensitivity. Air deflectors are available from sensor manufacturers and should be utilized in any areas where significant air flow is anticipated (such as air conditioner plenum applicaiion.s). Additionally, sensors should be located, whenever possible, in loca[ion.s which are relatively free from vibration and easily accessed for calibration and maintenance. Obviously, this carmot always be accomplished. It usually is difficult, for example, to locate sensors in the tops of compressor buildings at locations which are accessible and which do not vibrate. 

The main rises of a sintered metal flame arrester are in the sensing heads of flammable gas detectors and in flame arresters for gas welding (oxyacetylene) equipment. 

Optical fibre based optical detection systems offer a number of advantages over bulk optical sensing systems. The principal one is that a robust passive sensing head may be remoted from the monitoring station a factor giving particular advantages in severe environments. This also allows... 

The second box contains a peristaltic pump and a servoactuator. Both the pump and servo are controlled electrically from the sensing head and are powered from the same power supply. The separation of the sensing head from the pump and servo provide electrical and mechanical isolation and address space constraints associated with mounting the system on the autonomous underwater vehicle. The peristaltic pump enables operation at a variable flow rate and has bidirectional flow capability. The servo actuates a movable sample inlet tube that can be raised or lowered by remote control to enable precise positioning of the inlet relative to the source or in the source plume. 

The residual gas analyzer sensing head is generally supplied on an ultrahigh-vacuum flange which can be readily accommodated on most metal vacuum apparatus. 

Using a more complex electronic circuit, the zero pressure (with the sensing head at p < 10 3 mbar) may be compensated for with a zero-adjustment potentiometer. The required temperature of the wire (and hence S) is adjusted by another potentiometer (atmospheric pressure adjustment). By using these two potentiometers, adjustments can be made so that gauge heads are interchangeable and may be connected to any suitable power supply. 

Cold cathode, complete system with readout 820 Hot cathode, complete system with readout 1580 Radiation alphatron, sensing head and amplifier o give mV output, 2850,... 

This sensor is based on the comparison of the absorption of two x-ray beams, one of which is sensitive and the other insensitive to variations in particle size [19-21]. Each sensing head is specific to a particular system since the relationship between the two beams is dependent on the composition of the solids in the slurry stream. The technique is limited to x-ray opaque material. 

There are many gas-sensing head designs in use. However, they all conform to one of the basic designs shown in Figure 12.4. Type (a) represents the most... 

---