Applications Guide
140
Modline 5
8.5
Ratio Sensors
Modline 5 Series 5R Sensors utilize a dual detector assembly that measures temperature by comparing
infrared radiation levels in two wavelength bands (0.85 to 1.05 microns and a narrow band centered at
1.0 to 1.10 microns). They have the capability to measure temperature by comparing the relative infrared
radiance at two different wavelengths and computing the ratio of the two. Temperature readings are
based on the ratio of the two signals in these bands.
See Section 3
, page 22 of this manual for more information about signal reduction,
resolving targets and other factors about using ratio sensors.
8.5.1
E-Slope Settings
When using a Series 5R Sensor as a two color ratio Sensor you must properly select the E-slope value.
An E-Slope adjustment is provided to allow you to calibrate the Sensor to measure the temperature of
the target material accurately.
Series 5R Sensors are commonly used for applications involving materials in one of two main
classifications:
1.
Greybody materials have an Emissivity that is the same at both detected wavelengths.
2.
Materials with emissivities that are not the same at both detected wavelengths (a slope or variance
in the emissivity at the two wavelengths exists).
The first of these, the class of graybody materials, contains those materials that have emissivities that
are the same at both detected wavelengths. The most common graybody materials are described below.
When your target is made from any of these materials and are oxidized, set the E-Slope Control of the
Sensor to a value of 1.00.
Materials which require an E-Slope setting of 1.0:
Blackbody calibration standard.
Cavities in any opaque, isothermal body.
The following metals when worked in air are subject to oxidizing: Iron, Cobalt, Steel, Nickel,
and Stainless Steel.
The second main classification is a family of metals with emissivity that exhibit a non-linearity (or slope)
of approximately 1.06.
Materials which require an E-Slope setting of 1.6:
Clean, smooth, unoxidized surfaces of the following metals: Iron, Molybdenum, Molten Grey
Iron, Platinum, Cobalt, Rhodium, Nickel, Steel, Tungsten, Stainless Steel, Tantalum
If the materials in your process do not fall into either of these categories, you will have to test your
product to find the appropriate E-Slope setting. To do this, sight the instrument on a sample target
having a temperature that you have accurately determined by some other means (such as a reliable
thermocouple). For best accuracy, select a temperature near the center of the instrument's range, or
better still, carry out the test at several points throughout its range.
Adjust the E-Slope Setting until the indicated temperature matches the value you have previously
determined. Set the E-Slope control to this value whenever measuring this type of target. If you use
several tests, average the results and use the averaged value as your E-Slope setting.
