# Transparency Meter Calibration

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```					          Transparency Meter – Standard Procedure Calibration

Safety

Wear protective clothing and eye protection

Electrical hazards

A risk assessment must be carried out before starting this work

Calibration Procedure

Making and calibrating the instrument

1. Set up the electrical circuit as follows: -

The first decision to take is the value of the fixed resistor. You want the
voltage range across the fixed resistor to be as wide as possible. Set the
resistance substitution to 1000. Place the LDR at the end of the tube,
and put a 36W lamp at the other end. Record the voltage readings in this
light with the LDR uncovered.

2. Place 20 microscope slides between the lamp and the LDR, and take
output voltages

3. Change the value of the resistance substitution box, and repeat the
process (repeat this for a range of resistance values – this will give
you information about the best value fixed resistor to choose)
4. Calibrate your light meter by taking the reading with no microscope
slides as the brightest level (this calibration must be taken within the
tube, as it needs to take place in the dark) – this is your relative

5. Measure the distance between the lamp and LDR – this is distance X

6. Keep the LDR fixed in position, but move the lamp so the distance
separating it and the LDR is 1.4 X (the relative intensity at this point
is 0.5). Record the output voltage reading

7. Now move the lamp twice the distance so it is 2X (the relative
intensity at this point is 0.25). Record the output voltage reading, and
repeat for 3X; 4X and 5X – fill all your results in the calibration
results table similar to the one below (do this in excel as you will need

Distance (cm)           Relative intensity            Voltage (V)
X                          1
1.4X                        0.5
2X                        0.25
3X                        0.11
4X                       0.063
5X                        0.04

8. Plot a graph of relative intensity (x-axis) against the voltage across
the fixed resistor (V) (y-axis). This is your calibration graph

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 views: 15 posted: 5/29/2011 language: English pages: 2