ROCTEST FOP, Instruction Manual, Page: 23 / 29

E10160-200722 FOP
Page 20
Z All these digits serve to calculate the relation from cavity
length variation in nm to psi with the following equation:
psi
nm
in Slope ZZZ . Z
Y
   
2
10
4.1 Reading the FOP
Reading the pressure with the FOP is simply made by connecting the FOP, entering the
gauge factor and performing a NULL GAUGE in a fiber optic readout unit such as DMI,
UMI or FTI models. This will give directly the pressure in psi or bar depending of the Unit
System used.
In some particular applications and also for sensor troubleshooting, it is useful to have the
Fabry-Perot cavity distance in nanometers. To do so, the gauge factor 0001000, known
as the Default Gauge Factor, must be enter in the readout unit instead of the sensor gauge
factor (generally, it is already introduced in the readout unit and identified as FISO 1000).
4.2 Example
For a given FOP pressure sensor, the following readings can be taken.
A) Using the sensor Gauge Factor
Entering the gauge factor 6025192 and performing a null gauge before
applying any pressure leads to the following results:
Applied Pressure
(psi)
Measured pressure
(psi)
0 0
200 200
B) Using the Default Gauge Factor 0001000
Using the gauge factor 0001000 leads to the following results:
Applied Pressure
(psi)
Measured Cavity
Length (nm)
0 18190.5
200 17152.0