Galil has introduced a new version of its RIO smart I/O controller
which provides higher range and resolution of the analog inputs and
outputs. The new RIO-47120 provides 8 analog inputs and 8 analog
outputs with user programmable ranges of 0 to 5V, 0 to 10V, +/-5V and
+/-10V. The default analog resolution is 12-bits, with 16-bits
available as a factory option. The RIO-47120 has all the features of
the RIO-47100 but with this enhanced analog I/O capability. Both RIO
models combine analog and digital I/O with intelligent processing in a
compact, cost-effective unit.
On-Board Intelligence
Galil’s RIO controllers areintelligent I/O controllers with Ethernet communication. They can
operate as either a ModBus master or slave allowing them to communicate
with multiple devices including PLCs and Galil’s Ethernet motion
controllers. An internal RISC processor handles I/O logic with ease.
Features include arithmetic and logical processing, symbolic variables,
arrays, program memory with multitasking, event triggers, and email
capability. Galil’s two letter command language makes programming the
RIO quick and easy and a web interface is also provided for graphical
display of RIO status. The RIO is also fast, processing commands in
about 40 microseconds.
Analog and Digital I/O
In addition to on-board intelligenceand non-volatile memory, the RIO provides numerous analog and digital
I/O including 8 analog inputs, 8 analog outputs, 16 isolated inputs, 8
high power isolated outputs and 8 low-power isolated inputs. Multiple
RIO units can be connected to an Ethernet network allowing for simple
I/O expansion. The RIO can be powered by Power-Over-Ethernet (PoE) for
driving lower power devices, or an external 18-36 VDC supply can be
used.
Process Control Loops
A useful feature of the RIO whenworking with analog I/O is the internal process control loops complete
with PID filtering. These are handy for applications which require
tight control of an analog process such as temperature control. The RIO
provides special commands used for the process control loop as shown in
the Table below. The user can specify the set point with the PS command
and the loop rate with the CL command in addition to the PID
parameters. Process loop times as low as 1 msec can be programmed.
- Command
- Description
- AF
- Analog input for feedback
- AZ
- Analog output for control
- KP,KI,KD
- PID parameters
- IL
- Integrator limit
- DB
- Dead band
- CL
- Control Loop update rate
- PS
- Commanded set point
- TE
- Tell error
Example
Consider an example of a process control loop used toprecisely control the temperature of an oven. A temperature sensor is
used for the analog feedback. The RIO compares the set point with the
feedback and applies PID filtering to minimize the error. The resulting
analog output is then applied to the heater for closed loop control.
The figure below shows the block diagram of the closed-loop system.
Below is the actual RIO program for the temperature control.
- #Process
- CL 25; '25 msec update rate
- AF 0; 'analog input 0 as feedback
- AZ 0; 'analog output 0 as control
- KP 1; 'proportional gain to 1
- KD 10; 'derivative gain to 10
- KI .5; 'integral gain to .5
- DB .1; 'dead band of .1V
- PS 1.8; 'set-point at 1.8V
Note that CL sets the loop rate at 25 msec, although a slower
update rate could have been chosen due to the slow nature of the
temperature response. The set point is set at 1.8 Volts with the
command PS 1.8. The dead band command is used to prevent the system
from responding to minor disturbances.
