Things to Consider When Upgrading From Your Model 4421 to the Model 4421A Power Meter


If you caught our previous article/FAQ regarding the 4421 Power Meter Obsolescence Notice, then you may be considering your next steps for continued power meter measurement support. Along with some size differences, the 4421A Multifunction Power Meter is offered in five different model configurations, and the topics below are important to understand when you make your selection. 


Instrument Size Differences

The older 4421 was a 3U, half-rack form factor instrument with a handle that could be used to elevate on your desktop for better front panel viewing. 

The 4421A is optimized for operator interaction, armed with a large 9.7" full color LCD touchscreen display for easy readability. 

If your goal is to integrate the 4421A into a test system or calibration cart, know that it does have a rackmount kit accessory available. 


Type and Number of Sensors Supported

Like the 4421, the 4421A will interface with 4020, 4027A, 4027F, and 4028 Series sensors and uses the same latch-n-lock cable interface. There is no need to purchase all new sensors. 

Additionally, if you want to add a greater degree of accuracy (from 1% down to 0.5%) to your measurements, there is a model of 4421A that allows you to connect the 7027 and 7037 precision sensors via USB. 

The 4421A has model options that allow for up to two sensors to be connected at once. The variations possible are:

  • One latch-n-lock sensor
  • Two latch-n-lock sensors
  • One latch-n-lock sensor and one USB sensor
  • Two USB sensors

Depending on your configuration, you can view single or dual sensor power readings as well as plotted data on a graph. Note that even when two sensors are connected, you can opt to show only one of them at a time if you wish. 


Supported Communications Protocols

The 4421 offered both GPIB (aka IEEE 488) or RS-232 to allow you to connect to the meter from a PC and acquire measurements using your own automation software.

The 4421A has models which have both RS-232 and LAN that allow you to do the same. 


Programming and Automation Support

Using either of the communication protocols indicated above, the 4421A implements a SCPI (standard commands for programmable instrumentation) command set to allow for remote reading or monitoring of power measurements. You can use any programming language of your choice where the API allows for write, read, and query of commands. You can find programming examples in no less than Python and LabVIEW on Bird's GitHub repository for the 4421A Power Meter

If you have an existing program that automates the 4421 using its command set, know that the 4421A provides a "Legacy Mode" setting that will allow a subset of the 4421 commands to be used, meaning that there will be little to no need to update your code. However, because we have streamlined the number of commands it is recommended that you review the manual for what is supported. 



The 4421A features a large touchscreen display for monitoring up to two sensors simultaneously. You can build your own automation software in any programming language using the meter's SCPI command set and communicating over either LAN or RS-232. To simplify meter selection, you can use the flow chart provided below. 

With all that said, if you still wish to hold on to your older model 4421, know that you can find its datasheets and manuals on our Discontinued [Product] Manuals landing page.  

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