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The Challenge:  

Develop an application capable of exercising multiple Zinc Air Fuel Cells (ZAFC’s) while monitoring their performance and  logging all monitored process variables.

Figure 1. The performance and characteristics of multiple Zinc Air Fuel Cells running prolonged tests are made possible using  LabVIEW, the LabVIEW State Diagram Editor and NI-VISA 

The Solution: 

The LabVIEW State Diagram Editor was used to develop the structure of a LV 8.2 application that made use of set of reentrant drivers developed to control the Amrel loads that provided virtual loads required to test the fuel cells. Both automatic  and manual mode of operation were required to allow the users to test new products and design and to allow for customized  scheduling of load changes to simulated prolonged use.

Figure 2. Project specifications indicated that the ZAFC’s required a Manual Mode and an Automatic Mode of operation. The  application allowed the user to transition between these states at will. 

Abstract: 

During the design phase of the application, it was determined that each fuel cell had to be tested and monitored independently  of any other testing that may be taking place. It was also determined at design time that all of the functionality present in the  Manual mode of operation was required in the automatic mode. Another detail that required special attention was that all of  the electronic loads shared a single GPIB port as the communication medium. 

NI-VISA and NI-Spy Allow for Easy Driver Development 

NI-VISA was used to develop the interface drivers. The use of NI-VISA allowed for multiple communications sessions to be  active at the same time. NI-VISA’s tight coupling with NI-Spy allowed monitoring of the GPIB interactions during the initial  testing and debugging of the drivers.

Figure 3. The NI-Spy utility allows for the monitoring and logging of the communication details of NI-VISA. 

Once the details of the communications and functionality were tested and benchmarked, they were converted to re-entrant  VI’s to permit multiple ZAFC to be tested at the same without interaction between the controlling processes that will be  directing the testing. 

Manual Mode Code Development 

Since all of the functionality required in Manual Mode was required also required in Automatic mode, the Manual mode of  operation was developed and tested first. This approach allowed the common functionality to be tested and benchmarked and  refined once for both modes.

In the Manual Mode of operation, the application will first determine if the Amrel load is available and operational (Init). If  the preliminary check of the load failed an error flag will be set (in Set Init Error) and a graceful shutdown will be initiated  (Shutdown). If the initial checks showed no errors, the Manual Mode of operation will periodically transition between the  “What commands?” state and the “Time to Read?” states. 

The “What commands” state will determine if a command was issued by the GUI process and if will cause a transition to the  appropriate state (“Set output”, “Set Current”, or “Set Shutdown”) if a command was received. When no command is  received the “Time to Read?” state will be entered to determine if the state of the loads voltage or current should be updated.  Once the “Manual Mode” of operations was tested and found acceptable, the Automatic Mode of operation was developed  starting with a clone of the Manual Mode.

Figure 5. Auto mode. The automatic mode of operation was developed by using the Manual Mode as a starting point and additional states were added to support the automated schedule and to detect test end conditions.

Automatic Mode is an Embellished Form of the Manual Mode 

A careful comparison of the state diagram used for the Manual mode of operation (Figure 4) and the state diagram for the  Automatic mode will show that they share the same mechanisms for starting, handling user requests, error recovery and  shutdown. The new states (“Do POL Now?”, “Get POL”, and “Test Complete?” along with their ancillary states) implement  the scheduling and checks required to properly exercise the ZAFC and determine when the ZAFC has reached the end of its  life. 

Summary 

LabVIEW along with the NI-VISA, NI-Spy and the NI LabVIEW State Diagram Toolkit made the development of the “Zinc  Air Fuel Cell Test System” both fun and easy. Once one station was completed, the application was cloned to allow multiple  ZAFC to be tested 24 X 7. NI-Spy made it easy to develop the driver. The State Diagram Toolkit permitted the development  of a self-documented application that was readily converted for other use.