Remote LabVIEW via LV-Link

• Introduction
• Python implementation
  • configure
  • get value
  • set value
  • type check on Python
  • Special Notice: unsupported latch action
• LabVIEW implementation

Tips

source code in this tutorial

	lvlink_basic.zip

Introduction

Python implementation

configure

from lvlinkpy import Session

# Create a session. The argument is the lv-link port number asigned on LabVIEW.
s = Session(19810)
# Check control references
s.print_control_info()

LVLinkpy session constructed. Estimated latency is 0.00 ms
===================================
Boolean:{"_dim": 0, "_type": "?"}
Numeric:{"_dim": 0, "_type": "i4"}
String:{"_dim": 0, "_type": "U"}
Cluster:{"_dim": 0, "_type": "C"}
stop button without latch:{"_dim": 0, "_type": "?"}
===================================

get value

def get_value_tutorial1():
    # User can get the value from the name of the control.
    # Suppose there is a control called "Boolean" in the LabVIEW.
    print(s.get_value("Boolean"))
    # If the control name is incorrectly given, it will raise an error.
    print(s.get_value("fdzggZWSdgs"))

True
An exception occurred: KeyError – 'ValueName: fdzggZWSdgs is not a valid variable on server site.'
None

def get_value_tutorial2():
    # Almost the value type on LabVIEW is supported.
    print(s.get_value("Boolean"))
    print(s.get_value("Numeric"))
    print(s.get_value("String"))
    print(s.get_value("Cluster"))

True
810
qwerty
{'Array': [1, 2, 3]}]]

set value

def set_value_tutorial1():
    # User can set the value by the name of the control.
    # Suppose there is a control called "Boolean" in the LabVIEW, this code will set the control value to "True".
    s.set_value(valueName="Boolean", value=True)

type check on Python

def set_value_tutorial2():
    # This package will perform type check before send to LabVIEW.
    # So, If user send a string to a bool control, it will raise an error.
    # However, ignore_check=True can avoid type check on python.  This action may lead an error on LabVIEW.
    # Since the LV-Link server on LabVIEW will ignore the error, this code will not have effect.
    s.set_value(valueName="Boolean", value="string")
    s.set_value(valueName="Boolean", value="string", ignore_check=True)

An exception occurred: ValueError – the data type of the data(Boolean, type: U) does not fit to the origin data(type: ?). please check the data type or try to call update session function

Special Notice: unsupported latch action

def set_value_tutorial3():
    # mechaction=True argument can activate mechanical actions of the control.
    # (for example firing an event case)
    s.set_value(valueName="Boolean", value=True, mechaction=True)

def stop_vi():
    # there is a "Stop" button on LabVIEW. When setting it to True, LabVIEW VI will be stopped.
    s.set_value("Stop", value=True)
    # however, this button has a latch action and it is not supported on LV-Link
    # (including "latch when pressed", "latch when released", "latch until released")

    # set a stop button without latch action.
    s.set_value("stop button without latch", value=True)
    # in order to do the "button-click" functionally, we can use the mechaction with event case instead.

LabVIEW implementation