Instruction Manual for Low-E Coating Detector

     Theory of Operation

     Calibration

     Operating Instructions

     Limitations on Use

     Thresholding and Advanced Use

     Batteries

     Contact Information

The coating detector operates by shining infrared light into the glazing and measuring how much is reflected.  The infrared light emitting diode (IR LED) has a central wavelength of about 940nm.  This graph compares the spectrum of the light source to the three kinds of glazing the unit is designed to test. 

Calibration

The device needs to be calibrated at the beginning of each session or if there is a significant change in temperature. This is because the performance characteristics of some components are affected by temperature.

To calibrate:

1. Set both the "Mode" rocker switch to the "Calibrate" position and the "Power" rocker switch to the "On" position.

2. Place the mirror provided with the device, firmly against the detector window.
(see photograph at right)

3. Press and hold the "Test" button.

4. Using the flat screwdriver provided, adjust the "Cal. Adj." until the "Cal OK" light comes is on.  (see photograph at right)
(The light will be on for a small range of positions and ideally the trim pot should be adjusted so that it's position is the middle of this range.)

Once the unit has been calibrated, it is ready to use on a glazing system.

The "Low Batt." light may flash briefly during a measurement.  This is normal. The batteries may need to be replaced when the "Low Batt." flashes continuously. 

2. Hold the unit against the surface of the glazing.  The back side of the unit has the detector window and needs to face into the glazing.  Firmly place this entire surface flat against the window.

3. Push the "Test" button.

4.  Observe which of the three lights is illuminated.

5.  If possible, repeat the test from the opposite side of the glazing system.  

The primary intent of this device is to provide a quick means of verifying that a typical insulated glass residential window has a low solar heat gain low-emittance coating.  A "typical" window would be double glazed with glass layers around 3 mm thick and a gap width around 12 mm.  Any significant deviations from this configuration could produce erroneous measurements.  

The unit will work best when the coating is on the near pane (back side of the glazing layer that is in contact with the test device).  If the expected position of the coating is not known, it is recommended that this be determined using and a separate method (Eteckt or brightness of reflection in laser thickness device). 

   1.  Far pane measurements through thick glazing layers or across wide gaps.

   2.  Absorptive glazing layers or composition tints located between detector and low-e coating.

   3.  Applied films that are tinted.

   4.  Glazing layers that are not flat (e.g. automobiles, skylights).  Measure from concave side for best results.

   5.  Tempered Glass.  Measure coating on near pane for best results.

   6.  Highly deflected glazings. Measure at center of glass for best results.

The unit cannot produce a result for solar heat gain coefficient because it only measures in one region of the solar spectrum. 

Thresholding and Advanced Use

The three indicating lights, Clear, High Solar Gain Low-E, and Low Solar Gain Low-E, have been selected to come on at various levels of reflection. Thresholding refers to how the detector has been tuned to select which indicator light will turn on for a given level of reflection.  In these prototypes, thresholding is determined by fixed resistors on the circuit card.   The thresholding was selected somewhat arbitrarily since there is no standard definition of what constitutes a low solar gain coating.   The exact settings of the thresholding vary for different units because of differences in the performance characteristics of the emitters and detectors.    The average thresholding in percent reflection (at 940nm) is as follow:   0 to 6% reflection -- no indicator light, 6 to 17% -- "Clear", 17 to 36%-- "High Solar Gain Low-E", and 36 to 100% -- "Low Solar Gain Low-E."

It is possible to change the thresholding if the current thresholding is not working well for a particular glazing system.  For example, a glazing system with a low-solar gain low-e coating that had extraordinarily thick glass may be very close to the transition zone.  Unless you are really comfortable soldering on PCBs and have access to 1% resistors, the unit should be returned to LBNL to make changes to the thresholding.   

An option to changing the thresholding of the indicator lights is to monitor the voltage reading directly for a continuous indication of the level of reflection.  At the bottom of the unit are two contacts that provide a place for the user to measure the detector voltage signal.  Using a voltmeter (not provided), the user can monitor the level of reflection in greater detail than provided by the simple indicating lights.   This approach could be used, for example,  to differentiate between glazing systems that both yield the same indicator light in the simple test.  The voltage signal is 0 to 1 VDC.  Calibration adjusts the reading to 1 VDC for the mirror.    The baseline reading with no glazing system is not zero because of internal reflections.  Normalizing between the baseline reading and the calibration reading can yield the % reflection (at 940nm).

If the "Low Batt." light flashes continuously the batteries may need to replaced.  First, however, try turning the unit off and back on and see if the "Low Batt." still flashes.  If temperatures are very cold, the battery voltage could be low even though they don't necessarily need to replaced.

The batteries are located inside the unit.    Using the Phillips-head screwdriver provided, open up the case by unscrewing the four screws in the corners of the bottom of the case.  (see photo).  The inside of the unit is delicate but not dangerous. Loosen the Velcro holding strap, remove the four batteries.  Replace with new batteries and reassemble.