Thursday, July 27, 2017

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Quality Assurance

In order for PROFIBUS devices of different types and manufacturers to correctly fulfill tasks in the automation process, it is essential to ensure the error-free exchange of information over the bus. The requirement for this is a standard-compliant implementation of the communications protocol and application profiles by device manufacturers.

To ensure that this requirement is fulfilled, the PNO has established a quality assurance procedure whereby, on the basis of test reports, certificates are issued to devices that successfully complete the test.

The aim of the certification is to provide users the necessary security for error-free functionality during the common operation of devices of different manufacturers. To achieve this, the device undergoes rigorous practical testing in independent test laboratories. This enables early detection of any misinterpretations of the standards by developers, thus allowing remedial action by manufacturers before devices are implemented in the field. Interoperability of the device with other certified devices is also part of the test. Upon successful completion of the test, the manufacturer can apply for a device certificate.

Basis for the certification procedure (see Fig. 35) is the standard EN 45000. The PROFIBUS User Organization has approved manufacturer-independent test laboratories in accordance with the specifications of this standard. Only these test laboratories are authorized to carry out device tests, which form the basis for certification.

The test procedure and sequence for certification are described in the guidelines No. 2.032 (DP slaves), No. 2.062 (PA field devices) and No. 2.072 (DP master).

 

8.1 Test procedure

A precondition for the test is the assigned ID number and a GSD file, as well as an EDD for the device where applicable.

Device certification procedure

The test procedure, which is the same for all test laboratories, is made up of several parts:

The GSD/EDD Check ensures that the device description files comply with the specification.

The Hardware Test tests the electric characteristics of the PROFIBUS interface of the device for compliance with the specifications. This includes terminating resistors, suitability of the implemented drivers and other modules and the quality of line level.

The Function Test examines the bus access and transmission protocol and the functionality of the test device. The GSD is used to parameterize and customize the test system. The black-box procedure is used during testing, which means that no knowledge is required of the internal structure of the implementation. The reactions generated in the test specimen and their time ratios are recorded on the bus monitor. If necessary, the outputs of the test device are monitored and logged.

The Conformity Test forms the main part of the test. The object is to test conformity of the protocol implementation with the standard. Essentially, the test deals with the:

State machine: the PROFIBUS protocol is defined in the form of a state machine. All externally visible state transitions are tested. The target behavior is summarized in programmable sequences. The actual behavior is analyzed, compared with the target behavior and the result is written to the protocol file.

Behavior in the Case of Fault, which simulates bus faults, such as interruptions, short-circuits of the bus line and power failure.

Addressability: the test device is addressed under three arbitrary addresses within the address range and tested for error-free functionality.

Diagnosis Data: the diagnosis data must correspond to the entry in the GSD and the standard. This requires external activation of the diagnosis.

Mixed Operation: combination slaves are checked for correct functioning with an FMS and DP master.

Interoperability test: the test device is checked for interoperability with the PROFIBUS devices of other manufacturers in a multivendor plant. This checks that the functionality of the plant is maintained when the test device is added. Operation is also tested with different masters.

Each step of the test is carefully documented. The test records are made available to the manufacturer and the PROFIBUS User Organization. The test report serves as the basis for issuing a certificate.

 

8.2 Conformance Certificate

Once a device has successfully passed all the tests, the manufacturer can apply for a certificate from the PROFIBUS User Organization. Each certified device contains a certification number as a reference. The certificate is valid for 3 years but can be extended after undergoing a further test.

The addresses of the test laboratories can be obtained from the PROFIBUS Web site.

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