- General
System Operation
The height of the PA response peak indicates the strength of the PA
response and therefore how much oil is in the water. There are other
factors which affect the PA response such as pressure, temperature and
salinity. Separate pressure and temperature transducers are included
within the system. To obtain an estimate of the salinity, the time delay
from the pulse being fired to the PA response being received is measured.
The time delay allows identification of any change in the speed of sound,
termed the acoustic velocity and after correction for the process temperature
and pressure, estimation of brine salinity is possible. Laser diode
drivers of two commercially available wavelengths (currently 905 and
1550Nm) are used sequentially, in order to provide further information
on the fluid response.
-
The Oil in Water Monitor Prototype
Below is a block diagram of the oil in water monitor
:
The
head unit contains the laser delivery optics, piezo-electric acoustic
transducer (PZT), pre-amplifier and energy detection circuits and semiconductor
pressure and temperature transducer in a flanged duplex mounting rated
for working pressure up to 100 bar and process temperatures up to 100°C.
The pre-amplifier is required to be located near to the PZT, to reduce
signal attenuation and maximise signal to noise ratio. Mounting is by
a 3 inch ANSI B31.3 900# flange to a weldolet or tee branch. Installation
is recommended to be in a vertically upward flow stream.
Below is a detailed block diagram of the OIWM head unit.
Two
lenses focus the light just before the sapphire window into the fluid.
A beam splitter between these two lenses reflects a small proportion
of the light which is detected by a photodiode and used to monitor the
laser diode energy output.
The head unit is linked to the control unit by fibre-optics and signal
wiring. These are carried through armoured conduit. The control unit
contains the data processing, power supply, communications interfaces
and laser drivers for the system. The control unit determines and co-ordinates
laser firing and data acquisition, performs data reduction and outputs
processed data to the display unit over a serial communication link
using Modbus protocol.
Below are photographs of the OIWM:
Photograph
of OIWM Assembly
Photograph
of sensor head electronics
