A Comprehensive Comparison of Thermal Imaging Camera

With so many thermal imaging (or infrared) cameras to choose from, how do you select the one that best suits your needs? Our comprehensive comparison chart highlights the differences between the various models; however, what is the significance of the key features listed when it comes to making the right choice for you?

IR Resolution
IR resolution refers to the detector pixel resolution, as opposed to the LCD display resolution. Pixel resolution is the maximum number of display points on a screen. The more pixels, the
better the resolution, and the sharper the thermal image.

Thermal Sensitivity
Since what a thermal imaging camera does is take radiant thermal emergy and convert it into a visible image, the best we can “see” the thermal energy is limited by the number of pixels and the sensitivity to temperature differences that the camera can pick up. Typical thermal imaging cameras have sensitivities of 0.25°C to 0.05°C. The visual defined by 256 colors or scales of gray, leading by division to 256 different possible temperatures that can be displayed. Often, this result in the camera attempting to pick up and display temperature differences of narrower range than its thermal sensitivity. Thus a block of pixels is shown to be a blotchy, uniform mass of temperature, however, this is not the reality and the image is inaccurate. This result is known as “noise”. Image quality improves and noise decreases proportionally to an infrared camera’s thermal sensitivity. The smaller the thermal sensitivity, the lower the noise and the better the image will be.

Field of View (FOV)
Field of view defines the size of the area that is seen in the thermal image. Typically this is given in horizontal degrees by vertical degrees. The lens has the greatest influence on what the FOV will be. Instantaneous field of view (IFOV) describes the capability of a thermal imager to resolve spatial detail (spatial resolution). It describes the smallest object that can be seen at a given distance.

Temperature Range
Be sure that the temperature range the camera operates in is within the range of temperatures of the targets you will be measuring. Some cameras feature a temperature range that is suitable to industrial applications, others are better suited for home inspections.

Accuracy
For thermal imaging cameras, accuracy is the temperature range within which the reported temperature is statistically likely to be. The industry standard for consistent accuracy is ±2% or ±2°C, whichever is greater. Beacuse temperature measurements are based on the detection of infrared radiation, and in order to produce accurate and repeatable results, adjustments should be made for the following factors: (1) emissivity values below 0.6; (2) temperature variations of ±30°C (54°F); (3) making measurements beyond the resolution of the system (target too small or far away); and (4) field of view.

Built-in Illuminator Lamp
Infrared cameras can see in total darkness but visual cameras require well lighted conditions and high resolution to generate clear, sharp pictures. Make sure the visual camera in the thermal imager has a built-in illuminator lamp, otherwise you could have a hard time comparing the thermal image to the visual image.

Image Fusion
Simultaneously capture and overlay pixel-for-pixel infrared and visible light images for full image optimization with 5 different viewing modes.


1. Full IR: For troubleshooting and analyzing equipment and installations with very high resolution IR imaging. For detecting the smallest temperature variations to track down the origin of problems and fully document the extent of remediation. Full IR images are automatically linked to full visible light images.

2. Picture-in-Picture: For creating an IR window surrounded by a visible light frame to easily identify thermal anomalies, while maintaining a frame reference with surroundings.

3. Alpha Bending: For combining visible and infrared images together in any ratio to create a single image with enhanced detail that will help in precisely locating problems.

4. IR/Visual Alarm: For displaying only temperatures that fall above, below, or in between a specified range as IR image, leaving the rest of the scene as a fully visible light image.

5. Full Visible Light: A bright, detailed pixel-for-pixel reference image of subject areas for documentation and reporting.

Thermal Palettes
A palette is a color scheme used to display the thermal variations and patterns in a thermal image. Whether inspecting or analyzing, the objective is to select the palette that best identifies and communicates the problem. Ideally a thermal imager that allows the user to select or change the desired palette both in the camera and in the software should be chosen.
A wide selection of available color palettes allows the thermographer greater flexibility in thermal inspection, analysis and reporting.

Laser Pointer
The laser pointer keeps your hands free and clear from danger while allowing you to point to the area of concern. Best of all, the laser pointer will allow you to see precisely where the infrared camera’s lens is focused.

http://www.itm.com/attachments/pdfs/TI_BROCH_ENG.pdf

Temperature Measurement

Thermocouples


Thermocouples are sensors that measure temperature and pass that information to a control or monitor. Thermocouples are used in all types of applications, can measure wide temperature ranges, and are offered in a large variety of standard configurations.

Thermocouples are made of two dissimilar metal wires joined at their measuring end forming the "measuring junction" also known as the "hot junction". A small voltage, known as the Seeback voltage, is created at a junction of dissimilar metal alloys. This voltage changes as a function of temperature. See Fig. 1. The control or monitor measures this small voltage and converts it to a temperature signal. Modern instrumentation also measures the temperature where the thermocouple is connected to the instrument. This is the reference junctions. See Fig. 1. Any temperature effects near the instrument can be cancelled out leaving an accurate reading of the process to be measured. A thermocouple may be directly connected to a control or monitor. Extension wires, if used, must be of the same materials as the thermocouple wires.

Thermocouples designed with their measuring junctions in contact with metal surfaces are known as grounded junction thermocouples. These are the most common, generally have the fastest response times, and are the most economical. Ungrounded junction thermocouples offer the advantage of electrical isolation. Sensors are constructed with various types of protection/mounting hardware, extensions, and wire terminations. The sensor types and their temperature ranges are shown in the table below.

Fig. 1 Voltage Difference vs. Degrees F for J Type Thermocouple

RTDs

RTDs are usually platinum wire wound on a glass or ceramic bobbin and sealed with a coating of ceramic or glass. They can also be made by depositing platinum as a film on a substrate and then encapsulating it. The electrical resistance of the RTD channges as a function of temperature. Circuitry similar to a Wheatstone bridge is built into controls designed for use with RTDs. Constant current into the bridge produces an output voltage that varies with temperature. Lead wire resistance can significantly affect the RTD measurement. This is typically corrected using a third (compensating)
lead wire. See Figures 3 and 4. Extension wires used with RTD's may be plain copper wire. RTDs are generally more accurate and more stable over time than thermocouples. Dwyer RTDs are built to rigorous DiN (most common) or NIST standards and are defined in a wide variety of standard configurations.

Thermistors

Thermistors have a semiconductor material which changes its electrical resistance as a function of temperature. Extension wires used with thermistors can be plain copper wire. Thermistors offer accuracy similar to RTDs wihin narrow temperature ranges near ambient temperature. They also generally offer faster response times. Since thermistor standards vary, care must be taken to match the instrumentation to the sensor.

Temperature Limits

Sensor selection depends on two separate temperatures: process temperature and connector temperature. Make sure the local temperature at each component does not exceed the maximum rate service temperature for that component. Service Temperatures:

Stainleass Stell Tubing/Protection/Mounting Hardware: 1500°F
Stainless Steel Springs: 1500°F
Incon el Springs: 2100°F
Fiberglass Insulated Extension Wire•: 900°F
Junction Box (BX) Connector: 400°F
Plug: 300°F
J Type Thermocouple Junction: 1600°F
K Type Thermocouple Junction: 2500°F
E Type Thermocouple Junction: 1800°F
DIN or NIST RTD: 1607°F

Sound Level Meter

Weighting

The system whereby a sound level meter
differentiates decibel levels from among three frequency groups -
high, middle and low.

A Weighting

Weighting that attenuates lower frequencies to approximate the response
of the human ear.

 B Weighting

Gives combined decibel readings of
 high-frequency and mid frequency noise levels. Use in conjunction with A weighting to isolate the sounds that are causing a problem.

 C Weighting

Reads all frequencies the same but gives a better response to higher frequencies than do A or B weightings. Use to pinpoint problems when A or B weighted scale readings are very high.

PSI to Engineering Units

Looking for PSI to engineering conversions? Check out the linked PDF!

http://www.itm.com/attachments/pdfs/pressure_conversions.pdf

Pressure Terminology & Definitions

Gauge Pressure: Pressure measured relative to ambient atmospheric pressure. Referred to as pounds per square inch (gauge) or psig.
 
Absolute Pressure: Pressure measured relative to high vacuum. Referred to as pounds per square inch (absolute) or psia.
 
Vacuum: Vacuum measured relative to ambient atmospheric pressure. Referred to as pounds per square inch (vacuum) or psiv, or inches of mercury (Hg) vacuum.
 
Differential Pressure: Pressure measured relative to a reference pressure. Referred to as pounds per square inch (differential) or psid.
 
Pressure Transducer: Provides a linear DC voltage output proportional to applied pressure.
 
Pressure Transmitter: Provides a linear current output proportional to applied pressure.
 
Proof Pressure: The maximum pressure that may be applied without physical damage to the sensing element.
 
Burst Pressure: The maximum pressure that may be applied without physical damage to the sensing element.
 
Accuracy: Combined error of linearity, hysteresis and repeatability.
 
Linearity: The maximum deviation of any calibration point, on a specified straight line, during any one calibration cycle.
 
Hysteresis: The maximum difference in output, at any measured value within the specified range, when the value is approached first when increasing and then decreasing pressure.
 
Repeatability: The ability to reproduce output readings when the same pressure value is applied consecutively, under the same conditions, and in the same direction.
 
Excitation: The external electrical voltage and/or current applied to a transducer for its proper operation.
 
Ambient Conditions: The conditions (pressure, ,temperature, etc.) of the medium surrounding the case of the transducer.
 
Response Time: The length of time required for the output to rise to a specified percentage of its final value as a result of a step change in pressure.
 
Thermal Error: The maximum change in output, at any pressure value within the specified range, when the temperature is changed from room temperature to specified temperature extremes.
 
Thermal Sensitivity Shift: The sensitivity shift due to changes of the ambient temperature from room temperature to the specified limits of the operating temperature range.
 
Thermal Zero Shift: The zero shift due to changes of the ambient temperature from room temperature to the specified limits of the operating temperature range.