SCADA Component:
Field Instrumentation
Field Instrumentation refers to the
devices that are connected to the equipment or machines being controlled
and monitored by the SCADA system. These are sensors for monitoring certain
parameters; and actuators for controlling certain modules of the system.
These instruments convert physical
parameters (i.e., fluid flow, velocity, fluid level, etc.) to electrical
signals (i.e., voltage or current) readable by the Remote Station equipment.
Outputs can either be in analog (continuous range) or in digital (discrete
values). Some of the industry standard analog outputs of these sensors
are 0 to 5 volts, 0 to 10 volts, 4 to 20 mA and 0 to 20 mA. The voltage
outputs are used when the sensors are installed near the controllers (RTU
or PLC). The current outputs are used when the sensors are located far
from the controllers.
Digital outputs are used to differentiate
the discrete status of the equipment. Usually, <1> is used to mean EQUIPMENT
ON and <0> for EQUIPMENT OFF status. This may also mean <1> for FULL
or <0> for EMPTY.
Actuators are used to turn on or
turn off certain equipment. Likewise, digital and analog inputs are used
for control. For example, digital inputs can be used to turn on and off
modules on an equipment. While analog inputs are used to control the speed
of a motor or the position of a motorized valve. |
