Lens Calibration Kit

PN0498

Optotherm thermal imaging cameras are calibrated at Optotherm prior to shipment. Thermal camera calibration involves the following:

  1. Pixel response non-uniformity compensation throughout ambient operating range.

  2. Sensor radiometry correction

  3. Lens uniformity correction

  4. Lens radiometry correction

The first two items can only be performed at Optotherm.  The last two items, however, can be performed in the field using the [PN0498] Lens Calibration Kit and Lens Calibration software within Thermalyze.

Applications

  • Calibrate new lenses in the field

  • Improve lens calibration in the field

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Overview

Specifications

Setup

Operation

Troubleshoot

Maintenance

    Overview

Included Components

  • HH804 RTD Thermometer

  • PT100 sensor

  • Blackbody Surface 60x60mm

  • Thermal pad

  • Heat shield

Required Products

Related Products

Manufacturer Information


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    Specifications

Omega HH804

Electrical
Temperature Scale
 Celsius or Fahrenheit user-selectable
Measurement Range
 Pt385(100 Ω) -200°C to 800°C, (-328°F to 1472°F) Pt3916/Pt3926(100 Ω) -200°C to 630°C, (-328°F to 1166°F)
Resolution
 0.1°C or 0.2°F
Accuracy
 Accuracy is specified for operating temperatures over the range of 18°C to 28°C (64°F to 82°F), for 1 year, not including RTD probe error. ±(0.05% reading + 0.2°C) on °C scale ±(0.05% reading + 0.4°F) on °F scale
Temperature Coefficient
 0.1 times the applicable accuracy specification per °C from 0°C to 18°C and 28°C to 50°C (32°F to 64°F and 82°F to 122°F)
Input Protection
 24V DC or 24V AC rms maximum input voltage on any combination of input pins
Maximum Differential Common Mode Voltage (Maximum Voltage between T1 and T2 during measurement)
 1 volt
Reading Rate
 1 reading per second
Input Connector
 Accepts for RTD 3 wires or 4 wires sub-miniature 4-Prong type connectors (flat blades spaced 7.9mm, center to center)

Environmental
Ambient Operating Ranges
 0°C to 50°C (32°F to 122°F) <80% R.H.
Storage Temperature
 -20°C to 60°C (-4°F to 140°F) <70% R.H.

General
Display
 4½ digit liquid crystal display (LCD) with maximum reading of 19999
Overload
 “----.-” or “OL” is display
Battery
 1.5V x 4 PCS (SIZE AAA) UM-4 R03
Battery Life
 200 hours typical with carbon zinc battery
Reading Rate
 1 time per second
Auto Power Off
 30 minutes, press power key to resume operation
Dimensions
 160mm(H) x83mm(W) x 38mm(D)
Weight
 Approx. 260g including batteries
Safety
 CE

XF-935-FAR PT100 Sensor

Sensor type
 Platinum Resistance Pt100 Ohms
Construction
 Thin film, platinum film on ceramic substrate
Temperature Range
 -50°C to +250°C
Extended lead wire configuration
 4 wire
Extended Lead Wires
 Teflon® insulated, stranded conductors
Ice Point Resistance
 100Ω Ohms
Fundamental Interval
 (0°C to 100°C): 38.5Ω nominal
Tolerance Class
 Class A
European / British Standard
 Conforms to IEC 60751:2008 / BS EN 60751:2008

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    Setup

Lens Installation

  1. Install the lens to be calibrated on the thermal camera.

  2. Make sure that the installed lens is selected in Thermalyze.

Thermoelectric Chuck Temperature

  1. Set the thermoelectric chuck to 20°C.

    Required Equipment: The Optotherm thermoelectric chuck (or other temperature controlled surface) is required in the following procedures.

Calibration Plate Setup

  1. Place one of the thermal pads on the thermoelectric chuck.

  2. Remove any protective packaging from the calibration plate and place (black side up) on the thermal pad.

    Do not touch the black painted surface of the calibration plate. Doing so will change its emissivity properties and non-radiometric thermal images may result.

  3. Insert the RTD sensor in the calibration plate side hole.

RTD Thermometer Setup

  1. Install the included batteries in the back of the Thermometer.

  2. Insert the RTD sensor connector into the input labeled "T1" on the top of the RTD thermometer.

  3. Turn on the RTD thermometer.

  4. Press button #2 to select the °C temperature scale.

  5. Press button #4 to select the T1 input for the large upper display.

  6. Press button #5 to set the RTD type to Pt385.

Figure 1: HH804 RTD Thermometer

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    Operation

 

Lens Uniformity Correction Lens Radiometry Correction Enable Lens Calibration

Lens Uniformity Correction

Procedure: Lens calibration is an intricate process involving rigorous procedures and requiring accurate temperature measurements. If the instructions in this manual are not followed precisely, non-radiometric thermal images may result.

Do not touch the black painted surface of the calibration plate. Doing so will change its emissivity properties and non-radiometric thermal images may result.

Thermal Camera Position

Position the thermal camera directly above the calibration plate at the distance listed in the table below.  Distance is determined by the lens installed.  Distance is measured from the front of the lens housing to the top surface of the calibration plate. If calibrating the Macro lens, adjust the focus ring to closest focus by turning the ring full clockwise (from the front of the camera). This distance deliberately places the calibration plate out-of-focus to prevent imperfections on the plate from affecting uniformity correction.

IS640 lens Uniformity Correction Distance
Macro 30mm
80µm
 50mm
40µm
 35mm
20µm
 40mm
5µm
 30mm

Thermalyze Software: See Thermalyze Operation documentation for Lens Calibration software features and operation.

Software Setup

  1. Start Thermalyze.

  2. Select the Calibration Range to calibrate.

  3. Start capturing thermal images.

  4. Open the Lens Calibration window (see Figure 1) by selecting the Lens Calibration item under the Setup menu.

  5. In the Create Low Noise Image group box, make sure Quadrant Average and Noise Reduction are unchecked.

  6. In the Lens Calibration Settings panel, uncheck Enable Lens Calibration.

Figure 1: Lens Calibration window

Create Low Temperature Image

  1. Make sure the thermoelectric chuck is set to 20°C and allow the calibration plate temperature to stabilize by observing the RTD Thermometer readings.

  2. Click the Reset button to remove any previously accumulated images.

  3. Make sure the thermal camera and lens temperature are stable by confirming that the lens name field background is green.  This field will be yellow if nearly stable and red if unstable.

  4. Press the large green button to the ON state to start accumulating images.  Accumulated images are averaged together to create a low noise image.

  5. Press the button to the OFF state after at least 500 images have been accumulated.

  6. In the Low Temperature Image panel, set Scene Temp to 20°C.

  7. Click the Set to Memory button.

  8. Click the Save Image to File button.

Create High Temperature Image  

  1. Set the thermoelectric chuck to the temperature listed in the table below.  Temperature is determined by the lens installed and current calibration range.  Allow the calibration plate temperature to stabilize by observing the RTD Thermometer readings.

  2. Click the Reset button to remove any previously accumulated images.

  3. Make sure the thermal camera and lens temperature are stable by confirming that the lens name field background is green.  This field will be yellow if nearly stable and red if unstable.

  4. Press the large green button to the ON state to start accumulating images.  Accumulated images are averaged together to create a low noise image.

  5. Press the button to the OFF state after at least 500 images have been accumulated.

  6. In the High Temperature Image panel, set Scene Temp to the thermoelectric chuck temperature.

  7. Click the Set to Memory button.

  8. Click the Save Image to File button.

IS640 Lens
 		High Temperature Image
Macro
 Low Range: 40°C
High Range: 50°C
80µm
 Low Range: 40°C
High Range: 50°C
40µm
 Low Range: 40°C
High Range: 50°C
20µm
 Low Range: 40°C
High Range: 50°C
5µm
 Low Range: 50°C
High Range: 60°C


Lens Radiometry Correction

Calibration Plate Setup

Place the heat shield on the calibration plate and position it so that the hole in the shield is in the center of the plate.  The heat shield will limit lens heating and reduce calibration inaccuracy.

Thermal Camera Position

Position the thermal camera directly above the calibration plate at the distance listed in the table below.  Distance is determined by the lens installed.  Distance is measured from the front of the lens housing to the top surface of the calibration plate. If calibrating the Macro lens, adjust the focus ring to focus on the calibration plate. This distance places the calibration plate in focus.

IS640 Lens
 Radiometry Correction Distance
Macro
 100mm
80µm
 69mm
40µm
 27mm
20µm
 31mm
5µm
 19.5mm

Thermalyze Software: See Thermalyze Operation documentation for Lens Calibration Points software features and operation.

General Software Setup

  1. Start Thermalyze.

  2. Enable Image Averaging and set to 32 images.

  3. Create a rectangle region in the center of the thermal image approximately 50 x 50 pixels.

  4. Select the Calibration Range to calibrate.

  5. Start capturing thermal images.

Lens Calibration Points Window Setup

  1. Open the Lens Calibration Points window (see Figure 1) by clicking the Lens Calibration Points button on the Lens Calibration window.

  2. In the Polynomial Fit panel, set Order to 3.

  3. Click the Delete All Cal Points button  to remove all obsolete calibration points.

Figure 1: Lens Calibration Points window

Enter Reading and Target Temperatures

  1. Set the thermoelectric chuck to the first target temperature listed in the table below.  Temperature is determined by the lens installed and current calibration range.  Allow the calibration plate temperature to stabilize by observing the RTD Thermometer readings.

  2. Make sure the thermal camera and lens temperature are stable by confirming that the lens name field background is green.  This field will be yellow if nearly stable and red if unstable.

  3. Click the Add New Cal Point button  to add a new row to the Temperature Calibration Points table. Note: To move the new row to the desired position, click and select the row to move and then click the Shift Cal Point Up  and Shift Cal Point Down  buttons.

  4. Enter the mean temperature value of the rectangle region (displayed in the Region Data Grid) into the Reading field.

  5. Enter the RTD Thermometer reading into the Target field.

  6. Return to step 1 using the next target temperature. Proceed to the next step after the last target temperature has been processed.

IS640 Lens
 		Target Temperatures
Macro
 Low Range: 10, 30, 50, 70°C
High Range: 20, 40, 60, 80°C*
80µm
 Low Range: 10, 30, 50, 70°C
High Range: 20, 40, 60, 80°C*
40µm
 Low Range: 10, 20, 30, 40°C
High Range: 20, 40, 60, 80°C*
20µm
 Low Range: 10, 30, 50, 70°C
High Range: 20, 40, 60, 80°C*
5µm
 Low Range: 20, 40, 60, 80°C
High Range: 20, 40, 60, 80°C*

* Higher target temperatures may be used depending on the temperature range of the thermoelectric chuck model. Note however, that high thermal stage temperatures may increase lens temperature, reducing calibration accuracy.

Create End Points

  1. End points are calibration points added to the beginning and end of the range of Target values and help prevent divergence of the polynomial curve fit at the curve extremes.

  2. Enter a value in the Target Temp field that is 10°C below the lowest target temperature in the table.

  3. Click the Create button to create and add the low end point to the table.

  4. Enter a value in the Target Temp field that is 10°C above the highest target temperature in the table.

  5. Click the Create button to create and add the high end point to the table.

Save Data

  1. Click the Set to Memory button.

  2. Click the Save Image to File button.


Enable Lens Calibration

Procedure

  1. Open the Lens Calibration window (see Figure 1).

  2. In the Lens Calibration Settings panel, check Enable Lens Calibration.

  3. In the Optical Correction panel, check Enable.

  4. In the Offset Correction panel, check Enable.

  5. In the Radial Correction panel, uncheck Enable.

  6. In the Optical Correction and Offset Correction panels, enter the appropriate values for the Scale Factor and Fine-Tune listed in the table below. Values are determined by the lens installed and current calibration range.

  7. In the Lens Calibration Curve panel, check Enable.

  8. Click the Save Settings to File button.

Figure 1: Lens Calibration window

IS640 Lens
 		Optical Correction Scale Factor
Offset Correction Scale Factor
Macro
 Low Range: 0.75
High Range: 0.6
 Low Range: 0
High Range: 0
80µm
 Low Range: 0.67
High Range: 0.52
 Low Range: 0
High Range: 0
40µm
 Low Range: 0.5
High Range: 0.5
 Low Range: -0.65
High Range: -0.52
20µm
 Low Range: 0.0
High Range: 0.0
 Low Range: 0
High Range: 0
5µm
 Low Range: 0.85
High Range: 0.85		 Low Range: 0.7
High Range: 0.7

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