Installation and Equipment - Thermal Imaging



Introduction

This page is dedicated to the Installation and Equipment of the Thermal Imaging method used at Iowa State University. It includes a detailed information of each part of the setup with its corresponding manual. The installation of each part and common problems are also presented. The thermal imaging setup consists of a recirculating chiller and booster pump that pushes cooled fluid through the stave core in an isolated acrylic box designed to house various imaging and sensing equipment.

Chiller

The chiller utilized is a SP Scientific-RC211B0 recirculating chiller. According to specifications the chiller can go from -80 ˚C to +75 ˚C. For more device information about the chiller click here, for the manual click here.

The fluid used in the chiller is 3M Novec 7100 engineered fluid. It has a boiling point of +61 ˚C and a freezing point of −135 ˚C. For more information on the fluid, click here

In operation, the chiller is set to −55 ˚C which gives a temperature around −40 ˚C at the stave and at +50 ˚C which gives a stave temp of around +50 ˚C. The chiller lacks the pump strength to move the fluid sufficiently through the piping system this requires a booster pump.

Booster Pump

The booster pump utilized is a Liquiflo-H5FSPP4B002606US booster pump, that has a pump motor PVN56T17V5338B that can be controlled by a Lenze-ESV751N02YXC EMA 4x inverter drive.

For more information on these devices look at the following manuals for the booster pump and the inverter drive.

In standard operation depending on the setting of the chiller and booster pump we attain different pressure values at the stave core. During normal operation, the RPM setting of the pump is set to 22.

Acrylic Box

An acrylic box is used to contain the stave core and isolate the device from outside thermal sources. The box is designed with a camera mount and two different setups.

One in which the camera is approximately 90cm above the core, allowing for a single picture with an 80 degree lens, and one with the camera 30 cm above it in which multiple pictures could be taken of the stave core close up and stitched together. It was decided for simplicity that the system will mainly be used with the full box mount allowing for a single picture per side of the stave.

When in operation, the box is sealed by using a rubber gasket around the main interchangeable parts and tape. Dry nitrogen is pumped into the box and two one way ports built on the opposite side allow the operators to decrease the humidity into the box. The box humidity must be kept under 1% during low temperature operation. Depending on weather conditions it may take over an hour to decrease the humidity in the box.

A 3D printed camera mount was made to hold the camera. It can be rotated allowing for alignment of the camera picture to the base of the stave.

An alignment wire is mounted in the bottom of the device. When connected to a DC power supply (around 5 V max), the heated wire can be seen by the camera allowing for pixel alignment with the camera.

Box isolation is required to ensure quality images. Though acrylic acts as a decent IR insulator, sources of heat from touching the sides of the enclosure to effects of cool air from the air conditioner can affect the thermal profile of the box. There by effecting the background of stave images.

Humidity and Temperature Sensors

Relative Humidity

The humidity of the box is measured using an Omega-HH314A humidity meter. The humidity inside the box must be kept around 1% inside the box otherwise frost will form at low temperatures on the stave core and the pipes.

Temperature

The main temperature reading device is the Omega-HH147U thermocouple temperature logger. Two Omega-TC-K-NPT-U-72-SMP pipe plug thermocouple probes are placed along the input and output pipes to the stave.

Two other thermocouples are used to measure the box temperature and the ambient room temperature. These devices are not connected anywhere in the box, often causing headaches when the internal one rests up against a heated or cooled part in the box causing it to be affected by the heat source.

Thermal Camera

The thermal camera is a FLIR A655sc. Three lenses have been tested 25, 45 and 80 degree lenses. The current method only uses the 80˚ lens (FLIR T198065). Specifications for the camera are

Specifications for FLIR A655sc
Temperature Range −40-650˚C
Measurement Accuracy +/-2% or 2C˚
Image Update Rate 50 frames per second
Detector 640x480 pixels
Spectral Band 7.5-14 μm

The software that controls the camera (Research IR) is used to create the images and calibrate the camera. When the camera is turned on it and the software is started the camera will auto calibrate but it is important to review the following.

  • Before turning on the chiller system, check that the background is uniform. When viewing an undisturbed box, the temperature across the stave and box should be uniform across the FOV with variations under 1C˚. If there is an odd background structure wait 30 minutes and see if it goes away. It is possible that the walls of the enclosure have slightly different temperatures, but they should still be uniform. If it persists it could be a problem with the camera-lens calibration. Try disconnecting and reconnecting the lens. When a lens is connected it recalibrates the camera to that lensí specifications.

  • The camera focus should be adjusted such that the stave is in focus.

  • The camera should be aligned using the heated wire built into the box, prior to stave installation.

  • Let the camera warm up before taking data (45 min). Under the control settings, turn off the auto NUC when you are taking data. The auto non-uniformity compensation function is applied to the camera based upon the camera temperature.

-- WilliamDaleHeidorn - 2017-09-13

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Topic revision: r6 - 2017-09-26 - WilliamDaleHeidorn
 
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