Williamson Two-Color (TC), Dual-Wavelength (DW) and Multi-Wavelength (MW) pyrometers include a series of advanced signal conditioning functions collectively known as ESP Filtering. This advanced signal conditioning feature allows these Williamson pyrometers to recognize valid measurement conditions and to make an active measure of temperature only when these valid measurement conditions exist. This advanced signal conditioning feature is patented by Williamson Corporation and is available only with Williamson pyrometers.
In addition to the measured temperature value, Williamson TC, DW and MW pyrometers measure two extra parameters: Signal Dilution (infrared energy) and Signal Strength (emissivity). For many measurement conditions, these extra measured parameters differentiate between a valid measurement condition and an invalid measurement condition. Invalid measurement conditions may result from any number of interference sources, such as an intermittent view of the measured target, an intermittent view of a flame, an intermittent hot background reflection, or an intermittent optical obstruction. For each of these interference sources, one or both of these extra measured parameter values almost certainly will be outside of the normal or expected range. The pyrometer makes a real-time measure of temperature only when both the signal strength and signal dilution measured parameters are within the range of valid measurement conditions. When the measurement conditions are outside of the valid range of measurement, the ESP Sample and Hold parameter or any of the Williamson Temperature Hold functions may be disabled or enabled, depending upon the desired pyrometer response. The function of each parameter is further described in the table below.
Common Industry Examples
Steel Hot Rolling Mill:
The pyrometer may view a reflected image of the heat energy emitted by a steel strip or plate before or after the intended target is within the field-of-view. This reflected image may introduce a false temperature reading; however, associated with this false reading is a very low Signal Dilution (infrared energy) signal.
- Solution: Enable the Signal Dilution Filter and Set the Low SD Limit to a value higher than is produced during the interference.
Aluminum Flame-Fired Billet Furnace:
A reflected image of the hot refractory walls of the billet furnace is observed off the surface of the highly reflective aluminum billet until the furnace door closes. This reflected image introduces a false temperature reading; however, associated with this false reading is a high Signal Dilution (infrared energy) signal.
- Solution: Enable the Signal Dilution Filter and Set the High SD Limit to a value lower than is measured during the interference.
Aluminum Forging Press Die Temperature:
The forging press-die intermittently opens and closes, and when the die is open, the aluminum billet, the formed aluminum part and flame is alternately present, preventing the aluminum infrared temperature sensor from observing a continuous view of the die. However, the measured Signal Dilution (infrared energy) value is lower when viewing the aluminum billet, the forged aluminum part and when the die is closed, and it is higher when viewing a flame.
- Solution: Enable the Signal Dilution Filter and set the Low SD Limit to a value ½-way between the typical values observed when viewing the die and when viewing the hot aluminum billet, and set the High SD Limit to a value ½-way between the typical value observed when viewing the die and the flame. Finally, enable the ESP Sample and Hold feature and the pyrometer will produce a continuous and stable temperature reading as the die opens and closes, and as intermittent interferences pass in front of the pyrometer.
Steel Foundry Auto Pour:
The measured temperature value when viewing a flowing stream of molten metal can be influenced by misalignment, the presence of over-pour and the intermittent presence of flames, severe puffs of smoke, and reflections off nearby surfaces; however, the measured Signal Strength (emissivity) value, typically in the 0.20 to 0.40 range, rises above 0.55 whenever these interferences occur.
- Solution: Enable the Signal Strength Filter and set the High SS Limit to a value of 0.550. This will prevent the pyrometer from making a false reading during the intermittent interference. Similarly, enable the Signal Dilution Filter and set the Low SD Limit to a value higher than the reading when heavy smoke interference introduces a false measurement. If desired, Enable ESP Sample and Hold to provide a continuous temperature reading or Enable “Temperature Hold” and select “Peak Hold” – Time Reset to hold the measured temperature values for a specific period of time.
Flame-Fired Pipe Annealing Furnace:
The product passes through the flame-fired heat treating furnace in a lateral motion, meaning that the product is intermittently within the pyrometer’s view. When the pyrometer is not viewing the pipe it is viewing the furnace floor. The customer wishes to have a continuous measure of temperature for automatic feedback control.
- Solution: ESP Filtering is not required. In the heating zone, the furnace floor is hotter than the temperature of the pipe. Enable Temperature Hold and select Valley Hold – Temperature Reset, and select a threshold temperature value ½-way between the temperature of the pipe and the temperature of the furnace floor. In the soaking zone and the cooling zones, the furnace floor is cooler than the pipe. Enable “Temperature Hold” and select “Peak Hold” – Temperature Reset, and select a threshold temperature value ½-way between the temperature of the pipe and the temperature of the furnace floor.
Induction Heat Treating:
A high-frequency induction heating system with a poor ground system induces a spike in the pyrometer reading when the power is first turned on. Once the part begins to heat, the pyrometer reads correctly, but the spike at the beginning of the heating cycle causes the on-off control relay to trip, stopping the heating process before it begins; however, the false reading produces a low Signal Dilution value.
- Solution: Enable the Signal Dilution Filter and set the Low SD Limit to a value higher than is produced by the interference. The interference will be eliminated and the pyrometer will not measure until the part begins to heat.
Induction Billet Furnace:
The pyrometer views a reflected image of the hot billet before it enters the field of view, resulting in a false reading. In addition, the temperature of the billet is not uniform across the length of the billet, with the corners being hotter than the bulk metal temperature. The recommended solution is to measure the center of the billet while it is still inside the induction coil (either viewing the center of the side of the billet by viewing through the coil windings or viewing the center of the end of the billet by viewing into the exit of the induction furnace) because this permits feedback temperature control for each individual billet in addition to also eliminating the referenced common interference. Because this is not always possible or desirable, sometimes it is necessary to measure the side of the billet after it has exited the induction furnace and the recommended solution is to measure the temperature of the billet more than 30 seconds after it has exited the induction heating furnace after the temperature of the corners has had a chance to cool. Again, this is not always possible, and advanced signal conditioning is required to eliminate this type of interference.
- Solution: There are two options to address these issues:
1. This is the preferred option when surface scale does not introduce a significant error in the pyrometer reading
Enable “Temperature Hold” and select “Valley Hold” – Temperature Reset, then select a threshold temperature about ½ of the way between the billet temperature and the bottom end of the range of the pyrometer and lower the Average Time to Disabled. This will select the coolest temperature along the length of the billet, which will usually represent the center of the billet.
2. This is the preferred option when surface scale may produce an artificially low temperature reading at some point along the length of the billet
Enable the Signal Dilution filter and set the Low SD Limit to a value higher than the reading during the reflection interference. Set the Average Time to a period of time equal to ½ to 2/3 the length of time that the billet is viewed by the pyrometer, set the Temperature Reset to Resume, and set the Signal Dilution Average Time to 0.1 seconds. Finally, enable “ESP Sample and Hold”. This will provide an average temperature reading for each billet and this value will be held between billets. Because the average time is shorter than the length of time viewing each billet, the temperature rise at the corner is averaged into the measured temperature for the bulk of the billet, and the temperature rise for only one corner is included at one time. This will produce a much more stable temperature reading compared to Peak Hold because the peak hold feature would select the hotter temperature of the corner, which is more variable and which does not represent the true bulk temperature of the billet.
Consult with one of Williamson’s Temperature Experts
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