Transcript Control & Output with LabVIEW

Control & Output with LabVIEW
Thursday, Feb 2nd
LabVIEW DAQ Output for Voltage,
Sensor Excitation,
and Control Systems
Part 1:
A Brief History of Some LabVIEW
Stuff You’ve Done So Far in ME-241
LabVIEW Application (Review)
• LabVIEW can work with Data Acquisition (DAQ)
Platforms in order to capture signals from a variety
of instruments.
• These include the instruments you have used so far
in ME241, such as:
Thermocouples, Pressure Transducers, Load cells,
Strain gages (& anything that uses a Strain gage)
Linear Variable Differential Transformers
LabVIEW Application (Review)
• We capture data in the form of electrical signals
by wiring our instrument into a DAQ device.
• These devices include boards that plug into the PC
via a USB-port or…
• More sophisticated devices that use PCI cards
inside a PC that plug into some benchtop device.
LabVIEW Application (Review)
The DAQ devices allow us to capture signals from
a given instrument. These instruments allow us
to measure the physical phenomenon that we
are interested in.
LabVIEW VI Creation
In class and laboratory we have used LabVIEW to
write virtual instruments (VIs).
We typically write a VI so that it can “talk” to the
outside world (the experiment on the bench).
In order to do this we use the DAQ Assistant.
LabVIEW VI Creation
We use the LabVIEW block diagram to create code
that measures, displays and records voltages….
The DAQ Assistant is key….
The DAQ Assistant allows us to tell LabVIEW
which channels on the DAQ device to sample.
For instance if we use a USB-6008 we might set
up four channels as follows…
This will yield data from 4 separate channels….
Part 2:
LabVIEW Can Generate Output!
DAQ Device Output
Most DAQ devices have the ability to generate
signals as well as collect signals.
The DAQ devices are able to do this via the port
they connect to via a cable.
Most standard DAQ devices can generate a signal
of 5-10 VDC.
This voltage is ample enough to power some
small transducers and instruments.
This is important to the proper collection of data.
Tank Draining Experiment Apparatus
• We use a battery to power the pressure
transducer. The battery provides 9 volts.
+
+
+
-
-
-
Tank
Pressure Transducer
Tube
9 VDC Battery Pack
Tank Draining Experiment Apparatus
Possible Alternative
• We could have used a DAQ Device to power the pressure
transducer
SCXI to PC
AO0
Tank
9 VDC Output
From DAQ Device
Tube
Pressure Transducer
• Advantage:
PC provides power. Batteries not needed. Power provided is “steady.”
Voltage Output
• The BASICS:
Most DAQ devices have the ability to produce
their own signals.
We can use these signals to interact with the
experiment or equipment we are using.
We can use these signals to power equipment.
We can use these signals to trigger events and
make stuff happen.
Part 3:
HOW do I make a DAQ device
provide a voltage???
• The BASICS:
LabVIEW Application
You need 3 things…..
MAX
DAQ Device
Voltage Output
Note the ANALOG side of
the USB devices near your
computers.
There should be terminals
labeled AO0 and AO1
AO stands for Analog
Output.
Most of the NI devices have
at least 2 such terminals
For output we wire a
terminal and a ground.
Voltage Output
• We access the analog output functions via
LabVIEW. To do this we can access the DAQ
Assistant.
• We can right-mouse click and access Functions on
the Block Diagram.
• Select the DAQ Assistant on the OUTPUT Menu
Voltage Output
• When the DAQ Assistant is selected you get 2 choices:
• “Acquire Signals”…what we have used so far
• “Generate Signals” choose this one for voltage output!
• Once you select Generate Signals choose Voltage
• The device or devices will appear. Choose either one
or both channels (depending on how many signals
must be generated.)
DAQ Assistant for Voltage Output
Compare Differences/Similarities
Build a Control to Dial 0-5 volts
On the Front Panel place a dial.
Connect this to “data’ on the Output DAQ Assistant.
Build a Control to Dial 0-5 volts
Turn the knob to some arbitrary value and press
the run arrow.
This vi will produce…
We can confirm this value by adding an INPUT
DAQ Assistant.
Build one that reads from input channel AI1.
Add a graph or indicator to your vi to show
output.
Exercise:
Build A VI to Generate an Output
and
Collect that Voltage as an Input
Part 4:
Applications and
Demonstrations
DEMO Application 1
• Sometimes we need more than just 5 or 10
volts
• How can the LabVIEW output function help us
to run a pump or motor?
Application: We need to use LabVIEW to control
a motor. The motor uses a variable voltage
from 60 to 120 volts to adjust from top speed
to low speed.
DEMO Application 1
In this case we would use a device with the
motor’s manual control electronics.
The controller will accept a grounded DC signal
and generates a proportional output voltage.
This output can be supplied to the speed setting
circuit of the motor’s controller.
This will drive the motor at a speed proportional
to the signal that LabVIEW sends to it.
DEMO Application 1
Turn-Table with experiment
Main power supplied
By 120 VAC outlet
0-10 VDC “control” volts from LabVIEW
Control box
With SCR-based
potentiometers
Power line
from control
Drive Motor
Turntable Control Application
DEMO Application 2
Using LabVIEW with advanced NI hardware.
In this example we want to send simple
commands to control the speed of a stepper
motor.
We will use a PCI-card in the PC, a “smart”
encoder/motor power board, and LabVIEW
software.
Demo Application 2
stepper
Coil wires
SCXI cable
PCI-card
LabVIEW Control VI
Demo Application 3
• Use LabVIEW to send
commands and receive
data from a balance.
• In this case we have no
DAQ or PCI cards
• We can only use the
PC’s serial port to “talk”
to the balance.
Demo App 3: Balance vi
• To use a “stand-alone” instrument like the
balance we have to:
• 1. write a vi that talks to a serial port
• 2. wire up a cable per the manufacturer’s
The vi
specs
reads…
0.847 g
PC
0.847 g
Cable has 2 RS-232 (9 pin) connectors
Balance
Demo Application 3
• In this case we will “write” data to the balance
using LabVIEW.
• LabVIEW will assign the serial port to transmit
data (Tx) and commands to the balance.
• The balance will use the same port to send
(Rx) data and information.
• In this case we will use a vi called a binary
converter in order to write between LabVIEW
and the balance.
DEMO Application 4
• Using LabVIEW with non-NI hardware.
• In this example rather than control voltage
directly via a DAQ we will send commands
directly to circuit boards.
• As in the Balance DEMO we will use only the
serial bus to link LabVIEW with the circuit
boards.
• HOW can LabVIEW talk directly to a circuit
board?
DEMO Application 4
• We talk to the circuit board by using “OpCode.”
• Op-Code will serve as a bridge between
LabVIEW and the binary assembly language
that a circuit board expects to see.
DEMO Application 4
Think of it as translation…
English
Spanish
“Good Morning” “Buenos Dias”
LabVIEW
“G-Code”
PC Interface
“Op-Code”
Irish
“Dia duit!”
Circuit Board
“Assembly”
DEMO Application 4
PC with LabVIEW
Serial Communications Card
Power Supply
24 VDC
0-15 volts
Power Board with SCR-based Transformer
Train Track