【正文】 s thermal processes and before and after drying. The smart sensors are configured on a highspeed multidrop work (defined below) and are individually addressable from the remote supervisory puter. Measured temperatures at all sensor locations can be polled individually or sequentially。 the data can be graphed for easy monitoring or archived to document process temperature data. Using remote addressing features, set points, alarms, emissivity, and signal processing, information can be downloaded to each sensor. The result is tighter process control. Remote Online Addressability In a continuous process similar to that in Figure 2, smart sensors can be connected to one another or to other displays, chart recorders, and controllers on a single work. The sensors may be arranged in multidrop or pointtopoint configurations, or simply stand alone. In a multidrop configuration, multiple sensors (up to 32 in some cases) can be bined on a worktype cable. Each can have its own “address,” allowing it to be configured separately with different operating parameters. Because smart sensors use RS485 or FSK (frequency shift keyed) munications, they can be located at considerable distances from the control room puter—up to 1200 m (4000 ft.) for RS485, or 3000 m (10,000 ft.) for FSK. Some processes use RS232 munications, but cable length is limited to 100 ft. In a pointtopoint installation, smart sensors can be connected to chart recorders, process controllers, and displays, as well as to the controlling puter. In this type of installation, digital munications can be bined with milliamp current loops for a plete allaround process munications package. Sometimes, however, specialized processes require specialized software. A wallpaper manufacturer might need a series of sensors programmed to check for breaks and tears along the entire press and coating run, but each area has different ambient and surface temperatures, and each sensor must trigger an alarm if it notices irregularities in the surface. For customized processes such as this, engineers can write their own programs using published protocol data. These custom programs can remotely reconfigure sensors on the fly—without shutting down the process line. Field Calibration and Sensor Upgrades Whether using multidrop, pointtopoint, or single sensor works, process engineers need the proper software tools on their personal puters to calibrate, configure, monitor, and upgrade those sensors. Simple, easytouse data acquisition, configuration, and utility programs are usually part of the smart sensor package when purchased, or custom software can be used. With field calibration software, smart sensors can be calibrated, new parameters downloaded directly to the sensor’s circuitry, and the sensor’s current parameters saved and stored as puter data files to ensure that a plete record of calibration and/or parameter changes is kept. One set of calibration techniques can include onepoint offset and two and threepoint with variable temperatures: ? Onepoint offset. If a single temperature is used in a particular process, and the sensor reading needs to be offset to make it match a known temperature, onepoint offset calibration should be used. This offset will be applied to all temperatures throughout the entire temperature range. For example, if the known temperature along a float glass line is exactly 1800176。F, the smart sensor, or series of sensors, can be calibrated to that temperature. ? Twopoint. If sensor readings must match at two specific temperatures, the twopoint calibration shown in Figure 3 should be selected. This technique uses the calibration temperatures to calculate a gain and an offset that are applied to all temperatures throughout the entire range. ? Threepoint with variable temp