Nulling the 301

How to Zero or Null a 301 densitometer before using it for density readings.Calibrating (Nulling) the 301

When the instrument is first turned on it must be zeroed (nulled) before taking measurements. To perform this task proceed as follows:

Nulling the instrument

• Turn on the instrument; Allow approximately two minutes for the unit to stabilize.

• Take a reading with no film (read air).

• While holding the "READ" button... press and release the "NULL" button, the instrument display should reads 0.00.

• A second reading should be taken with no film to verify that the unit is holding zero.

 Calibrating / Setting the instrument's slope

• Locate the Calibration Reference film and the small screwdriver.

• Turn on and zero (null) the instrument as described above.

• Measure the CAL step of the supplied film.

• If the measurement differs from the certified strip value by more than ±0.02D use the small screwdriver to increase or decrease the unit's slope untill it agrees,

• Again zero the unit... and follow by again reading the CAL step... repeat this zero/measure/cal/zero/measure sequence until the unit is accurately reporting the calibration density.
  
  After adjusting to the cal step read the other 4 steps, they should fall into the +/-.02 tolerance if you have a linear unit.   

NOTE:  If the unit does not read zero after several attempts at nulling, and the light source has been verified, there is an internal failure and the unit must be returned for repair.   It is recommended that the calibration / verification be performed once a week. More frequent verification can be performed if required by local regulations.