Redundant pressure sensors

The loo2 stracture is composed of two elements coimected in parallel so that each can perform the sub-system fimctioiL Under normal conditions of use, both chaimels request the safety function. A dangerous failure in both chaimels would result in the safety function not being processed correctly. The result of aity diagnosis test does not alter the outcome of the loo2 majority logic. It corresponds to the operation of two channels in parallel for the transmission of safety information (e.g. two redundant pressure sensors, two closing valves in series, etc.). 

Assemble the components into the process system and apply FMEA techniques to determine if protection devices on some components provide redundant protection to other components. For example, if there are two separators in series, and they are both designed for the same pressure, the devices protecting one from overpressure will also protect the other. Therefore, there may be no need for two sets of high pressure sensors. 

Another method to process and detect faulty responses of the redundant sensor signal is called the likelihood test. The likelihood test used is borrowed from nuclear reactor safety for pressure sensors deciding shutdown or no shutdown. Instead of shutdown or no shutdown for this case, the sensor reading would be rejected or accepted. For accuracy of the readings, the test chosen needs to reject readings that have even the smallest likelihood of being false and leading to the patient s inappropriate response.36... 

The best correction to these problems is not always obvious. In the first example of the heat exchanger, a pressure sensor with redundancy features could be installed between the primary and secondary loops such that when the positive pressure differential falls below a stipulated value (well above the point at which the pressures are reversed), operations should be shut down and the secondary loop emptied. A better solution would be for the heat exchanger to incorporate an intermediate loop so that the secondary and primary sides could not be directly coupled. 

A sensor whose causality cannot be inverted is usually a hardware redundancy, i.e., there is/are one or more sensor(s) whose output can be used to obtain the measurement of the redundant sensor [3, 5]. For example, a fluid-level sensor in a storage tank and a pressure sensor at the bottom of that tank produce correlated measurements and one of them is a redundant sensor. It must be noted that the causality of the output port of sensors, which may be connected to controllers, is never inverted. The following five compositions are possible in sensor causalities ... 

The diagram shows a schematic from the Siemens-Moore Safety Critical Transmitter Note how a redundant and diverse measuring system is used to compare the internal values of the pressure sensor. Diagnostics driven by the PES section will shutdown this transmitter into a fail-safe state if a defect is found. 

A regulator is a compact device that maintains the process variable at a specific value in spite of disturbances in load flow. It combines the functions of the measurement sensor, controher, and final control element into one self-contained device. Regulators are available to control pressure, differential pressure, temperature, flow, hquid level, and other basic process variables. They are used to control the differential across a filter press, heat exchanger, or orifice plate. Regulators are used for monitoring pressure variables for redundancy, flow check, and liquid surge relief. 

As you can tell from the above discussion, it is very easy to be fooled by a diflerential pressure measurement of level. As one who has been bitten many times by these problems, I highly recommend redundant sensors and judicious skeptism about the validity of instrument readings. 

In order to ensure an adequate quality of products and a safe operation, the monitoring of a batch reactor should include, at least, online measurements of temperature, pressure, and of some composition-related variables. In this context, online measurements may be defined as measurements obtained via instruments strictly connected to the reactor and characterize by response times markedly smaller than the characteristic times of the chemical reaction. In general, this is the case of temperature and pressure, which can be easily measured online by means of reliable, relatively cheap, and poorly intrusive sensors. This allows the introduction of sensor redundancy, a common practice to increase reliability. On the other hand, online... 

An alarm should sound any time redundant inputs disagree. In most cases, the operating personnel will have to decide what to do. In some cases the computer control system will have to decide by itself what to do if redundant inputs disagree. The more hazardous the process, the more it is necessary to use multiple sensors for flow, temperature, pressure, and other variables. Since it must be assumed that all measuring devices will fail, they should fail to an alarm state. If a device fails to a nonalarm condition, there can be serious problems. It is also serious if a device fails to an alarm condition, and there is really not an alarm condition. This is generally not as serious as the first case, but it can provide a false sense of security. Usually it is assumed that two... 

These cabinets are automated-purge cabinets with redundant safety features such as excess-flow sensors, reduced-flow orifices, and system-failure shutdown protocols. They utilize high-turbulence constmction with high exhaust flow—200 cubic feet per minute at 0.02 inches of water pressure differential. These are monitored by automated sensors and manometers with a visual readout at the cabinet location. All cabinets contain fire sprinklers (Figures 8.15 and 8.16). 

A large gas line is present in the top cover to duct dilution gas, noncondensable offgas, and steam to the adjacent quench tank. The quench tank provides a mass of water to condense transported steam and to cool other gases. Condensate spills over and is collected in the overflow tank. The quench tank has a cooling coil to maintain the water inventory in a subcooled state. The cooling coil, quench tank, and overflow tank are instrumented with flowmeters, thermocouples, level sensors, and pressure transducers in order to monitor the transient state of the system and extract the necessary heat balance information. Downstream from the quench tank is a spray tank which performs a redundant quench/gas cooldown function. While adding redundancy, the use of two quench tanks in... 

The Project shall comply with the Prometheus Single Point Failure Policy as documented in the Prometheus Project Policies Document 982-00057. (Level 2 Requirement) Structure and thermal management subsystems must be designed with fault tolerant capacity. This would include features such as ability to react flight loads in presence of element failure (with reduced margin) and redundant heaters and temperature sensors. Micrometeoroid and orbital debris protection reduce the risk in areas where single point failure can not be eliminated, such as the pressure boundaries. 

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