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Migrating from the 34401A RS-232 Serial Interface to the Truevolt DMM 34461A USB/LAN Interface - Migration Guide

Technical Overviews

Keysight Technologies

Migrating from the 34401A RS-232 Serial Interface to the Truevolt DMM 34461A USB/LAN Interface

Migration Guide

Introduction

The 34461A DMM is the next generation of 34401A that is a virtual drop-in replacement for 34401A. RS-232 is no longer being offered as an interface on newer instrument. For example, the 34461A does not support RS-232 interface and GPIB is optional on the 34461A. You may have difficulty when you want to upgrade your system with newer instruments which the instrument I/O interface is not compatible with your system controller’s RS-232 serial I/O. This note explains how to migrate the 34401A programming via RS-232 to the new 34461A DMM programming with VISA via USB or LAN interface with faster measurement speed.

The 34461A Truevolt DMM is a next generation DMM intended to replace the 34401A. Unlike the 34401A, the 34461A does not have an RS-232 IO interface. LAN and USB are standard, and GPIB is optional with the new 34461A DMM. This can present a challenge when upgrading your system with newer instruments whose IO interface is not compatible with the system controller’s RS-232 serial IO. This guide explains how to migrate existing 34401A programs developed for the RS-232 interface for use with the USB and LAN interfaces.

Tip 1: Use RS-232 to Ethernet converters for RS-232 controller to communicate with LXI instruments

Users who want to continue to use an RS-232 controller to communicate with their instruments can use RS-232 to Ethernet converters permanently mounted to the system controller. Connect the RS-232 to the controller side and the LAN to the 34461A DMM. This implementation is simple and effortless, as you do not need to rewrite the program to compensate for I/O interface changes.

Additional tips for the solution

The IP address of the DMM must be in the same IP address range of the converter. Even with the same subnet mask, there is problem to get the converter to communicate with the DMM using the DMM's default Auto-IP address of 169.254.4.61. You need to set the IP address to be within the same range as the default settings of the converter at 192.168.0.35 - to put it onto the same subnet. This means to set the address to 192.168.0.xxx, where xxx is any number between 0 and 255.

  • Converter settings take longer than expected to be applied. After settings are changed, communication with the DMM is delayed – giving the impression that some settings may be incorrect. The converter for example, did not apply the target IP address for 2-3 minutes - after which communication was restored.
  • This solution should not require IT approval for using the DMM's Ethernet port. Since this is a direct connection from the PC to converter to the DMM, all Ethernet traffic is isolated to the converter and DMM.
  • Using the converter with DHCP has not been tested. Most applications that require RS-232 have direct connections from the controller to instrument. However, it is believe that DHCP mode would work provided that the IP address of the DMM/instrument is static so that you can configure the converter's Target IP address. Use of DHCP and your LAN might require IT department approval.

Tip 2: Simple changes on the codes for programming with VISA via USB-TMC interface

You do not need to rewrite the programs when you migrate from the 34401A to 34461A DMM. The 34461A was designed to ensure it will work with SCPI commands that were written for 34401A. If you do not want to invest in a converter, only minor changes to the test program is needed to support the different instrument I/O interface. Follow the simple steps below; using VISA to communicate over USB to the instrument.

Conclusion

You can easily migrate from a 34401A to the Keysight 34461A Truevolt DMM with just a few simple steps, even if using an RS-232 serial IO port. Additional benefits of the USB interface are that it provides a robust and easy connection for the 34461A, and faster reading rates compared to the RS-232 serial interface.

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