Volume 1, Number 1 January 2002
TNT Tip: Device to Hold Hot UV Lamps
Holding a hot UV light at the required distance to accurately measure output is difficult, especially if there are several lamps and various specifications to meet. We have four working black lamps in our lab - the type with a woods filter and retaining ring. Each must be measured for output at monthly intervals to meet national standards and client specifications such as:
- 800 µW/cm2 @ 400 mm
- 1,000 µW/cm2 @ 380 mm, 400 mm, and the working distance
- 500 µW/cm2 @ 460 mm
Different methods to hold the lamps were tried. Retort stands and clamps, sticky tape, and sky hooks couldn't reliably reproduce the test situation for measuring output.
Here's a fix. This simple and easily made device can:
- hold the lamp at the required distance,
- be used at various distances, and
- reliably reproduce the setup for measurement on a regular basis.
It can also be used for different types of lamps including new air-cooled units.
Materials:
- coffee can - 1 kg size with 6 in. (150 mm) rim
- plywood base - 14 ´ 14 ´ 2 in. (350 ´ 350 ´ 50 mm)
- hardwood upright - 2 ´ 2 ´ 19 in. (50 ´ 50 ´ 500 mm)
- 3 No. 8 countersunk woodscrews - 4 in. (100 mm)
- 2 No. 8 roundhead woodscrews - 1 in. (25 mm)
- matte black paint - 0.5 pint (200 mL)
- wood of varying thicknesses for shims
Method:
- Remove base from coffee can and smooth down rough or sharp edges left by can opener.
- Using three large screws, attach upright to base as shown in sketch.
- Attach can to stem as shown using two small screws.
- Paint complete unit, including inside of can, with matte black paint.
- Project vertical centerline of can down to base and mark a cross.
- Cut wood shims of different thicknesses to alter distance between baseboard and base of lamp.
Procedure:
- Set lamp in holder.
- Allow lamp to warm up for 20 min.
- Place light meter on baseboard in center of cross.
- Vary distance with shims.
- Record output of lamp.
Reviewer's Note: There is a slight increase in the reading when using the can (which has 14 corrugations). A borderline call might be best checked without the lamp holder.
Con Murren
Ayrshire, Scotland
[ The NDT Technician ]
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