Instrumentation is the art of measuring the value of some plant parameter,
pressure, flow, level or temperature to name a few and supplying a signal that is proportional to the measured parameter.When engineers design a system that employs sensors, they mathematically model the response of the sensor to the physical parameter being sensed, they mathematically model the desired response of the signal-conditioning circuitry to the sensor output, and they then implement those mathematical models in electronic circuitry. All that modeling is good, but it’s important to remember that the models are approximations (albeit usually fairly accurate approximations) to the real-world response of the implementation. It would be far better to keep as much of the system as possible actually in the mathematical realm; numbers, after all, don’t drift with time and can be manipulated precisely and easily. In fact, the discipline of digital signal processing or DSP, in which signals are manipulated mathematically rather than with electronic circuitry, is well established and widely practiced. Standard transformations, such as filtering to remove unwanted noise or frequency mappings to identify particular signal components, are easily handled using DSP. Furthermore, using DSP principles we can perform operations that would be impossible using even the most advanced electronic circuitry.
standard sensors usually need to be physically close to the control and monitoring systems that receive their measurements. In general, the farther a sensor is from the system using its measurements, the less useful the measurements are. This is due primarily to the fact that sensor signals that are run long distances are susceptible to electronic noise, thus degrading the quality of the readings at the receiving end. In many cases, sensors are connected to the monitoring and control systems using specialized (and expensive) cabling; the longer this cabling is, the more costly the installation, which is never popular with end users. A related problem is that sharing sensor outputs among multiple systems becomes very difficult, particularly if those systems are physically separated. This inability to share outputs may not seem important, but it severely limits the ability to scale systems to large installations, resulting in much higher costs to install and support multiple redundant sensors.While sensors come in a variety of flavors (electronic, mechanical, chemical, optical, etc.), we’ll focus in this book on electronic sensor devices, for the simple but powerful reason that we can interface their outputs to a computing element (usually a microprocessor) easily. It’s the computing element that allows us to add intelligence to the sensor and, as we’ll see, that’s a very valuable addition.
Of all common environmental parameters, humidity is perhaps the least understood and most difficult to measure. The most common electronic humidity detection methods, albeit highly accurate, are not obvious and tend to be expensive and complex.
Accurate humidity measurement is vital to a number of diverse areas, including food processing, paper and lumber production, pollution monitoring and chemical manufacturing. Despite these and other applications, little design oriented material has appeared on circuitry to measure humidity. This is primarily due to the small number of transducers available and a generally accepted notion that they are difficult and expensive to signal condition.
Some of the more common ways of expressing humidity related information include wet bulb temperature, dew point and frost point. Wet bulb temperature refers to the minimum temperature reached by a wetted thermometer bulb in a stream of air. The dew point is the point at which water saturation occurs in air. It is evidenced by water condensation.
When temperatures below 0°C are required to produce this phenomenon it is called the frost point.
Humidity Sensors:-
RELATIVE HUMIDITY SENSOR HS 1100 / HS 1101:-
Based on a unique capacitive cell, these relative humidity sensors are designed for high volume, cost sensitive applications such as office automation, automotive cabin air control, home appliances, and industrial process control systems. They are also useful in all applications where humidity compensation is needed.Full interchangeability with no calibration required in standard conditions
● Instantaneous desaturation after long periods in saturation phase
● Compatible with automatized assembly processes, including wave soldering, reflow and water immersion
● High reliability and long term stability
● Patented solid polymer structure
● Suitable for linear voltage or frequency output circuitry
● Fast response time
● Individual marking for compliance to stringent traceability requirements
Humidity Transducer HX49
a controller/meter with an internal power supply, connect the controller/
meter input signal to the [+] terminal. Connect the controller/meter common to the [-]terminal.All transducers are factory calibrated to meet or exceed published specifications.
BIBLIOGRAPHY
1. “Humidity Sensors”—brochure describing Models PCRC-11 and PCRC-55 Relative Humidity Sensors. Phys-Chemical Research Corp.; New York.
2. “Humidity Measurement”—Instrumentation Technology; reprint P. R. Wiederhold. Available from General Eastern Corp.; Watertown, Mass.
3. “Handbook of Transducers for Electronic Measuring Systems”—Norton, Harry N.; Prentice Hall, Inc.; 1969.
4. “Electric Hygrometers”—Wexler, A.; NBS Circular 586; NBS Washington, D.C. 1957.
5. “An elegant 6-IC circuit gauges relative humidity”—Williams, James M.; EDN Magazine, June 5, 1980.
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pressure, flow, level or temperature to name a few and supplying a signal that is proportional to the measured parameter.When engineers design a system that employs sensors, they mathematically model the response of the sensor to the physical parameter being sensed, they mathematically model the desired response of the signal-conditioning circuitry to the sensor output, and they then implement those mathematical models in electronic circuitry. All that modeling is good, but it’s important to remember that the models are approximations (albeit usually fairly accurate approximations) to the real-world response of the implementation. It would be far better to keep as much of the system as possible actually in the mathematical realm; numbers, after all, don’t drift with time and can be manipulated precisely and easily. In fact, the discipline of digital signal processing or DSP, in which signals are manipulated mathematically rather than with electronic circuitry, is well established and widely practiced. Standard transformations, such as filtering to remove unwanted noise or frequency mappings to identify particular signal components, are easily handled using DSP. Furthermore, using DSP principles we can perform operations that would be impossible using even the most advanced electronic circuitry.
standard sensors usually need to be physically close to the control and monitoring systems that receive their measurements. In general, the farther a sensor is from the system using its measurements, the less useful the measurements are. This is due primarily to the fact that sensor signals that are run long distances are susceptible to electronic noise, thus degrading the quality of the readings at the receiving end. In many cases, sensors are connected to the monitoring and control systems using specialized (and expensive) cabling; the longer this cabling is, the more costly the installation, which is never popular with end users. A related problem is that sharing sensor outputs among multiple systems becomes very difficult, particularly if those systems are physically separated. This inability to share outputs may not seem important, but it severely limits the ability to scale systems to large installations, resulting in much higher costs to install and support multiple redundant sensors.While sensors come in a variety of flavors (electronic, mechanical, chemical, optical, etc.), we’ll focus in this book on electronic sensor devices, for the simple but powerful reason that we can interface their outputs to a computing element (usually a microprocessor) easily. It’s the computing element that allows us to add intelligence to the sensor and, as we’ll see, that’s a very valuable addition.
Of all common environmental parameters, humidity is perhaps the least understood and most difficult to measure. The most common electronic humidity detection methods, albeit highly accurate, are not obvious and tend to be expensive and complex.
Accurate humidity measurement is vital to a number of diverse areas, including food processing, paper and lumber production, pollution monitoring and chemical manufacturing. Despite these and other applications, little design oriented material has appeared on circuitry to measure humidity. This is primarily due to the small number of transducers available and a generally accepted notion that they are difficult and expensive to signal condition.
Some of the more common ways of expressing humidity related information include wet bulb temperature, dew point and frost point. Wet bulb temperature refers to the minimum temperature reached by a wetted thermometer bulb in a stream of air. The dew point is the point at which water saturation occurs in air. It is evidenced by water condensation.
When temperatures below 0°C are required to produce this phenomenon it is called the frost point.
Humidity Sensors:-
RELATIVE HUMIDITY SENSOR HS 1100 / HS 1101:-
Based on a unique capacitive cell, these relative humidity sensors are designed for high volume, cost sensitive applications such as office automation, automotive cabin air control, home appliances, and industrial process control systems. They are also useful in all applications where humidity compensation is needed.Full interchangeability with no calibration required in standard conditions
● Instantaneous desaturation after long periods in saturation phase
● Compatible with automatized assembly processes, including wave soldering, reflow and water immersion
● High reliability and long term stability
● Patented solid polymer structure
● Suitable for linear voltage or frequency output circuitry
● Fast response time
● Individual marking for compliance to stringent traceability requirements
Humidity Transducer HX49
a controller/meter with an internal power supply, connect the controller/
meter input signal to the [+] terminal. Connect the controller/meter common to the [-]terminal.All transducers are factory calibrated to meet or exceed published specifications.
BIBLIOGRAPHY
1. “Humidity Sensors”—brochure describing Models PCRC-11 and PCRC-55 Relative Humidity Sensors. Phys-Chemical Research Corp.; New York.
2. “Humidity Measurement”—Instrumentation Technology; reprint P. R. Wiederhold. Available from General Eastern Corp.; Watertown, Mass.
3. “Handbook of Transducers for Electronic Measuring Systems”—Norton, Harry N.; Prentice Hall, Inc.; 1969.
4. “Electric Hygrometers”—Wexler, A.; NBS Circular 586; NBS Washington, D.C. 1957.
5. “An elegant 6-IC circuit gauges relative humidity”—Williams, James M.; EDN Magazine, June 5, 1980.
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