Serial Instrument Control Tutorial

Publish Date: Feb 27, 2019 | 119 Ratings | 1.56 out of 5 | Print | 8 Customer Reviews | Submit your review

Table of Contents

  1. Overview of Serial Bus
  2. Connecting and Setting up a Serial Instrument Control System
  3. How to Create a VISA Resource for the Instrument in MAX
  4. Related Resources

1. Overview of Serial Bus

Serial is a common device communication protocol for instrument control because most computers and many remote instruments include at least one serial port. Single applications can be used across a variety of instruments with few modifications, reducing programming and test time.

For more information on the serial protocol, including information on transfer speeds and important parameters, please refer to Serial Communication Overview.


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2. Connecting and Setting up a Serial Instrument Control System

Engineers typically use serial to transmit American Standard Code for Information Interchange (ASCII) data. All data types are converted to strings of ASCII characters and then transmitted bit by bit across the serial bus. For two ports to communicate, both the instrument and the controlling computer must have the same baud rate, data bit size, stop bits, and parity.

A basic serial instrument control system consists of three parts:
1. PC (or controller) with a serial port
2. Serial cable
3. Serial instrument

As mentioned, most computers include a serial port. The only hardware setup required is connecting the serial cable to the serial port on the PC and the serial port on the instrument. The serial instrument may include some hardware drivers or software utilities for communication, and should include documentation on the baud rate, packet size, stop bits, and parity bits that the instrument will use. Additionally, check the National Instruments Instrument Driver Network to see if LabVIEW drivers already exist for your instrument, as well has tutorials on how to use them.

To confirm that the serial port on your computer is working properly, refer to Serial Communication Starting Point, to see how to perform a serial loop back test.


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3. How to Create a VISA Resource for the Instrument in MAX

With NI-VISA, communicating with your serial instrument is easy. To confirm that you are able to communicate with your instrument, open Measurement & Automation Explorer (MAX) found at Start>>Programs>>National Instruments>>Measurement & Automation.

Figure 1. MAX Main Menu

Expand the Devices and Interfaces subdirectory below My System. Below it you should see all the serial and parallel ports on your computer. In this example the computer has one serial port (“COM3”). Figure 2 shows the directory path to the serial port and the configuration window when COM1 is selected.

Figure 2. Serial Port Configuration Window

From this configuration window you can change the VISA Alias for easier identification and you can also communicate with your instrument through a VISA Test Panel by selecting Open VISA Test Panel. Your instrument should have specific commands for collecting and transmitting data and you can use the VISA Test Panel to test these functions and verify that they are working properly.

Using NI-VISA to Communicate with Your Serial Instrument

NI-VISA makes serial instrument programming fast and easy. VISA Open, VISA Read, VISA Write, and VISA Close are the basic VISA functions in LabVIEW used in the example VI in Figure 3. This example opens a VISA session to a serial device. A command is written to the device, and the response is read back. In this example the specific command being sent is the ID query for the device. Check with your device manufacturer for your device command set. After all communication is complete, the VISA session is closed.

Figure 3. LabVIEW Serial Program Using NI-VISA

NI-VISA provides built in serial examples to assist users with application design and development. 

  • Serial examples for LabVIEW can be found the in LabVIEW Example Finder by navigating to Help>>Find Examples>>Hardware Input and Output>>Serial. The Readme file for each NI-VISA version provides more information on where to find LabVIEW Serial examples. 
  • Serial examples for .NET, C and VB6 can be found by navigating to Start>>All Apps>>National Instruments>>NI-VISA Examples.


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4. Related Resources

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Customer Reviews
8 Reviews | Submit your review

good example  - Aug 5, 2017

I thought the example was useful and well explained. I'm new to LabView and I find the online help very good. It helps to have some programming experience in C, OOC or C++ for understanding the control/structure concepts. I used this example to query and communicate with one of my serial devices. :>

Indeed Helpful w/ requisite prior knowledge of LabView  - Jun 15, 2016

This short tutorial told me everything I needed to know re. the basics of setting up a serial instrument w/ NI-VISA. To the other commenters complaining of issues steming from lack of prior LabView knowledge, all I can suggest is looking at some more introductory LabView tutorials

All LabVIEW help from NI is useless  - May 26, 2016

I have spent a day just trying to tell the computer to set RS232 pin 3 high for a fixed pulse width every few minutes. Still can't do it. I have access to a LabVIEW developer level graduate and he has no clue.

Worthless  - Nov 23, 2015

So far most the documentation is designed for people who already know the answers. Too much "a priori" knowledge is assumed by the writer.

Almost Useless information  - Mar 16, 2012

This page doesn't describe the critical steps for creating controls on serial VISA.

This is Not a Tutorial  - Jul 11, 2011

This is not a tutorial. I know as little about VISA objects as I did before I read this page.

  - Aug 10, 2010

"A basic serial instrument control system consists of four parts: 1. PC 2. Serial cable 3. Serial instrument" What the ... ? For what is a fairly widely used communications method in industrial and research applications (which LabView targets) there is not much in this documentation. It also does not appear well reviewed as noted above.

insufficient documentation  - Oct 2, 2008

I am a novice user of LabVIEW and MAX. I could not make the VISA Test Panel work. There were no instructions for the many tabs and check boxes on the screen. There was no help function. Everything I tried failed.

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