Laserscale BS75A-R, Manual

Page: 24 / 56

22
4-3-1. Compensation Value
The hologram grating pitch P
G
of the scale is approximately
0.55
µ
m/22
µ
inch, while the detector signal pitch Ps is
theoretically 1/4 of it, that is 0.14 µ m/5.5 µ inch. This value
differs slightly from scale to scale. Therefore, it is necessary
to additionally make the pitch compensation for each scale,
in order to detect precise displacements.
The lowest four digits of the detector signal pitch for each
scale Ps = 0.1379
MMMM
µ m at 20 ° C/68 ° F show the
compensation value.
Be sure to set the display unit or detector to the
compensation value of the scale before operation.
When you operate the unit in an environment
where the temperature is not 20 ° C
To operate the unit in an operating temperature which is
not 20 ° C, adjust the compensation value as shown below
to make a temperature adjustment. The following
example shows the adjustment method for an operating
temperature of 23
°
C
Example:
The compensation value shown on the compensation
value label is
zxcv
.
0.1379
zxcv
× {1 × (23 − 20) × ( − 0.7 × 10
− 6
)}
= 0.1379
zx/b
Temperature difference from 20 ° C
Coefficient of thermal expansion of the scale
(see page 32)
The compensation value after temperature adjustment
will be
zx/b
. Set the display unit or detector to this
value.
4-3. Before Mounting
4-3-2. Compensation Value Setting
See the section “Compensation Value Setting” of the display
unit (BR series) or detector (BD series) operating manuals.
Note
The compensation values of the display unit (BR series) and
detector (BD series) are set to all zeros at the time of
shipment. In this state, the alarm sounds and you cannot
operate the unit. Be sure to set the display unit or detector to
the correct compensation value of the scale before
operation.