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For temperatures up to 60 deg.
C.,140 deg.F. all combinations of internally or externally
mounted sensors with integral or remote electronics may be
employed. For higher temperatures internally mounted sensors
should be specified with remote electronics. The standard maximum
temperature for internally mounted sensors is 120 deg.C., 244
deg.F. continuous immersion.
Externally mounted sensors may be used at up to 100 deg.C.,212 deg.F. with integral electronics and ,140 deg C.,282 deg.F. with remote electronics. Where a high temperature is part of the normal process conditions (as opposed to periodic during cleaning cycles for example), transmitters can be factory calibrated at actual process temperature.
For process temperatures beyond the above limits a sealed barrier assembly may be employed. A "non-rated" barrier diaphragm transfers the pressure signal via a filling fluid which is selected for its low coefficient of thermal expansion. This fluid transmits the process pressure to the sensor’s measurement diaphragm.
In this way temperatures of up to 500 deg C may be accommodated
In many applications, particularly shipboard, vibration is often an unknown quantity. Installation should follow good
engineering practices .
For external mounting instruments, flanged rather than threaded connections should be used and any stand off should be kept to the minimum length. Where a long stand offs are unavoidable additional webbing or bracing should be used.
Unsupported pole mount assemblies should be avoided where vibration is likely. Similarly equal precaution must be taken against forces being generated by tank stirrers or agitators.
PSM’s principle of measurement and the low mass design of the sensor, provides the best possible resistance to vibration effects and damage. The LVDT is sensitive to core movement in one plane only, giving increased stability under harsh conditions, and the fact that the diaphragm is in effect a spring, allows far greater tolerance of continuous vibration than with many "solid state type sensors".
The standard sensor construction materials of Hastelloy C276 diaphragm with 316 stainless steel body are compatible with wide range of process fluids. Where the medium is particularly aggressive the sensor can be manufactured with all wetted parts in Hastelloy and/or bodies manufactured in engineering plastics such as polypropylene or PVDF.
The sensor cable sheathing material is selected as appropriate for the intended duty. Options include general purpose polyethylene and a high performance "Hytrel" cable which is Marine Approved as low smoke, self-extinguishing. For internally mounted sensors in corrosive fluids the cable may require additional protection either by a rigid pole or flexible PTFE tubing.
In determining the optimum sensor type, the properties of the liquid should also be considered. Where the product is highly viscous or contains suspended solids, pockets or dead areas should be avoided and the mounting arrangement should be self draining.
The PSM sensor diaphragm lends itself to true flush mounting. This aspect is of particular importance for food or pharmaceutical applications and the sensor is offered with all recognised sanitary fittings to facilitate this.
