Carlin Component Testing - Manual (Page 7)

Carlin U – Residential Oil Burners – Page 79
Field testing a cad cell
Check room light resistance
1. With normal room lighting, the cad cell
resistance when in the open, as at right,
should be less than 10 kohms.
2. In the example shown, the resistance
measured 195.1 ohms. Notice that the
meter automatically adjusts the range
for the best reading. In this case, the
range shifted to ohms.
3. If the cad cell resistance is too high, try
cleaning the cell and measure the re-
sistance again. If resistance is still too
high, replace the cell.
4. If the cad cell resistance is below 10
kohms, perform a dark resistance test.
Check dark resistance
1. With the cad cell mounted inside the
burner, with no fl ame, the cad cell
should have very little light available.
The cad cell resistance should be at least
50 kohms.
2. The illustration on bottom right shows
a test of dark resistance by securely
covering the end of the cell. In this in-
stance, the cad cell resistance measured
82.2 kohms. (The meter automatically
changed the range to kilohms.)
3. If the cad cell resistance is below 50
kohms when the cad cell is mounted in-
side a closed burner with no fl ame, make
sure the combustion chamber is cool
and there is no stray light entering the
burner.
Light resistance:
Cad cell resistance in
room light
Dark resistance:
Cad cell resistance
with no light (or when
inside burner with no
fl ame)