MICRONOR AG
MR340-1 DIN Rail Module Controller
Page 20 of 74
Positioning the film affects the ultimate
performance of the system. Apply just
enough pull to the film so as it is stretched at
all times. Too much pull will increase pressure
on the read surface and may lead to high
wear of the film. Typically 50-100 grams of
pull force is sufficient.
When using a film with 0.4mm line spacing, it is posible to obtain 0.1mm resolution. Consult
Figure 15 below for recommended film strip dimensions. Each opaque and translucent cycle
will need to be a total of 400µm.
Figure 19. TD5334 Encoder Filmstrip dimensions
As can be seen in Figure 15, positional accuracy is given by the film itself and the shape of the
light beam. The film is made accurately to within ±3µm. The absolute edge accuracy is
approx. ±25% of the slit width. With the design, as shown above, the very worst case
deviation is ±50µm maximum. Typically ±25µm can be expected.
Thermal expansion of the film tape is typically 22µm/m/°C. With the temperature variation
within an MRI environment being minimal, this deviation is not a factor in accuracy when
operating at normal room temperature. The film base material is highly stable.
To obtain a balanced signal with a duty cycle of 50% and a phase shift of 90°, the distance
from the optical fiber to the film must be accurately controlled within the pick-up assembly.
This is a factory-only adjustment.
400µm
100µm
850nm
980nm