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4.
Turn purge gas pressure on and set the purge flow meter needle control valve to approximately 60 SCFH
(28 L/min).
5.
Apply power to the electronics module. “IR Temp” value will be displayed.
6.
Press the NEXT button to display the “Units” parameter.
7.
Press the UP or Down arrow buttons to toggle between Celsius or Fahrenheit and set as desired.
8.
Press the NEXT button to display the “4mA=” parameter.
9.
Press the UP or DOWN arrow buttons to set the temperature corresponding to 4.00 mA loop current.
10.
Press the NEXT button to display the “20mA=” parameter.
11.
Press the UP or DOWN arrow buttons to set the temperature corresponding to 20.00 mA loop current.
12.
Press the SAVE button to save all changes. The display will briefly indicate “Saving…”
Note:
If you do not press SAVE, the changes you made above will not be
remembered after a power fail.
13.
Press the NEXT button to display the temperature.
3.3 Ratiometric Two-Wavelength Sensing
The HIR ‘F range’ transmitter measures the intensity of light at two different wavelengths to determine the
temperature. This allows the measurement to be accurate even if there is a partial blockage of light due to
material buildup (occlusion) on the window or in the nozzle. In essence, the measurement is based on the light’s
color (wavelength), instead of the intensity, as is usually done with a single wavelength measurement. In addition
to the temperature, the amount of occlusion can also be measured as a Signal Value number from 0 (completely
blocked) and 100 (no blockage). The Signal Value appears on the display in small numbers below the
temperature. If the number falls below the Signal Alarm setpoint, then “LOW!” appears next to the displayed
signal level, and HART Additional Device Status Byte 1, bit 2 is set.
Note that below 1472 °F (800 °C), there is not enough infrared light at both wavelengths to make a two-
wavelength measurement. Therefore, temperatures between 662 °F and 1472 °F (350 °C and 800 °C) are only
measured with a single wavelength. In that case, the amount of blockage cannot be determined.
3.4 Preventive Maintenance
Model HIR is designed to give years of trouble-free operation without the need for service. In most cases, to
achieve this performance, the only requirement is that the optical path (nozzle, valve, window) temperature be
maintained above the freezing point of sulfur, and that the window purge be maintained to keep the window free
of particulates. Thus, a preventive maintenance schedule should include periodic inspections to verify that:
1.
The steam supply is on, the steam trap is functioning, and steam is heating the lens body,
2.
The lens purge flows at the recommended rate of 60 SCFH (28 L/min), and
3.
The thermal insulation as shown in Figure 1 is in place and in good condition.
Signal Strength Indication
Signal strength measurement (Signal=XXX.XX) is located beneath the temperature measurement when
displaying the temperature parameter. This value should read between 0 and 100 and indicates the amount of
light reaching the sensor relative to an unobstructed sight path. A value of ≥ 95 is normal. Values below 95 may
indicate the occurrence of sight path attenuation, possibly due to material build-up on window or inside the nozzle.
The signal strength should be monitored periodically. If it drops significantly or if the optical path temperature or
purge is suspected to be compromised, corrective action should be scheduled. This includes inspecting the
