Scentczar has focused on chemical detectors over most of our history. Many chemical detectors require a transducer or chemical sensor to convert chemical signal to electrical signal, as illustrated in figure 1, but there are interesting exceptions. Scentczar’s Miniature Passive Indicator, for example, uses a dot of dye on a substrate which migrates over calibration marks in response to hydrocarbon vapors – no batteries required. The sensor would be the dye spot and the detector would be the entire device including dye spot, calibration marks, and substrate. Figure 1 is sort of a canonical model for the chemical detector. In the model of figure 1 the detection system has to sample the environment or a process stream. Some systems are required to sample ambient air, an open path through ambient air, or a surface located in ambient air. Other systems require an inlet to match the ambient air, gas, or liquid stream to the detector system. For example, Scentczar worked on a fuel cell management system that required us to detect parts per million levels of carbon monoxide in a wet hydrogen stream, with no ambient air, coming from a catalytic converter. If the level of carbon monoxide went above a threshold the system would shut down the converter. Other process problems might involve detecting trace contaminants in a hydrocarbon stream or ammonia in an exhaust stack for example.
Figure 2 is a pictorial diagram of a modern chemical detector. With the magic of microprocessors there are not many components that go into a system. The system of figure 2 has a sampling head, an air moving system, chemical sensing cell which can be chosen from a range of technologie, and the rest is electronics. The power supply often consists of a switching power supply that powers the rest of the system. The largest power draw is frequently from heaters that may be required to keep the system at a constant temperature above ambient. Lightening protection is provided because the system may be installed in a remote box somewhere on a plant site.
Most chemical detectors start with a particular application and then are modified to serve other applications as the system gains acceptance in the market place and other customers with similar problems are identified. Frequently the original market is limited and will become saturated if the developer does not continually prospect for related markets. Thus the two most secure people in the organization are the marketing guru and the applications engineer. Figure 3 is an illustration of how this process works.
Figure 3 illustrates the normal course of events in a typical chemical detector business. The marketing guru spends his/her days out there visiting customers and attending trade events finding the latest problems to be solved. Once a likely candidate is identified the Applications Engineer mocks up the problem in the laboratory. If the mock up looks promising a prototype of the process is developed and tested. In the modern era of software the prototypes for a variety of customers can be quite similar. One of the advantages of dealing with the process industries is that plants tend to follow standard designs. For example there are two standard designs for oil refinery alkylation plants utilizing hydrogen fluoride. Once you’ve demonstrated your product with a standard design the next marketing chore is to identify all of the plants with that design for implementation. If you’ve left your first customer with a good feeling you’ve got an in with all the plants of similar design.
Much of the drive to develop chemical detectors since the 1950’s has come from three sources: 1) military requirements for chemical warfare detectors, 2) the oil refiners desire to switch from human sampling and laboratory analysis to real time analysis for the refining of fuel products, and 3) government regulation including EPA, OSHA, and mine safety requirements. A number of detector systems were developed by the military, in very expensive development programs, to detect chemical warfare agents and were later adapted to solve industrial problems. The petrochemical industry started with process gas chromatographs, which are considered process analyzers along with physical measurement systems, and are used to measure the distillation products of hydrocarbons. Much of the original process gas chromatograph work was done at Greenbrier Instruments in Lewisburg WVA. The plant has changed hands many times. A number of stand-alone chemical detectors have their start has gas chromatograph detectors.
All of the disciplines listed in figure 3 are needed in order to convert a chemical sensor into a useful chemical detector. Chemical Engineering is probably the least needed discipline because a customer usually has to develop a detailed specification including temperatures, pressures, flow rates, etc. A chemical detector is a complete system and requires an interdisciplinary approach.
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