Frequently Asked Questions

 

About the WITS Protocol

WITS Functionality

All WITS Devices provide a device profile XML file which specifies the WITS features supported by a particular version of the device.
It is important that a potential vendor incorporates all of the features that their potential buyer requires.
A tick list of features could be used for discussion.
Be aware that DNP is data hungry i.e. it puts a lot of bits on the wire. For example it requires verification dialogue.

This high level of data communication can slow things down when using GPRS or GSM.

 

WITS and the DNP3 standard

WITS is based on the DNP3 standard protocol. DNP3 provides generic mechanisms for the enhancement of the protocol in order to add functionalty, and WITS takes advantage of this to extend DNP3 to provide functionality identified and required by the UK Water Companies.
Group 0 attributes

WITS uses DNP3 Object Group 0 to provide asset management and interoperability of Field Devices through device identification (based on product manufacturer name, device type etc.). In particular WITS defines 2 attribute sets, the standard index 0 and a WITS attribute set.

standard DNP3 set
WITS set

Data Sets

state change events – Analogue Events, Counter Events, Binary Events

health check

application program management

callback requests

File Transfers

DNP3 File transfers are used to acccess Field Device log files, which store timestamped historical data. DNP3 File transfers are also used to provide Incremental configuration updates to Field Devices through a WITS defined file format.

bulk configuration
incremental configuration
data log

Secure Authentication

 

WITS Founder Vendors

The Founder Vendors are the technical team who developed the WITS protocol based on the industries requirements :-

Servelec
ITT Waste & Wastewater (now Xylem)
Schneider Electric
Serck ( now also Schneider Electric )
Technolog
NB: Metasphere were involved in the early design stages

 

Developing a WITS Compliant Device

Developing a device

Join the PSA which then provides access to the WITS Application Notes which provide the detailed technical information necessary in order to develop the WITS protocol for a WITS Master Station or Field Device.

The actual development process and tools are for the vendor to determine. A DNP3 stack is available from Triangle Microworks which is used by some vendors as the basis of their WITS device, while others have developed an in-house stack – either is acceptable as the only criteria is to demonstrate successful testing to the WITS standard.

Here is a most useful guide for vendors entitled “Steps to consider in implementing a WITS Field Device” – click here.

 

For a Field Device to be compatible with Master Stations that only support an older version of the standard the Field Device must also support the same version of the standard as the Master Stations. For example, the Field Device must generate incremental configuration files (during a configuration upload) and data log files in the format supported by the Master Station.

This can be achieved by have a setting within the Field Device that defines which version of the standard it will use (this could be stored within the Bulk Configuration File) or alternatively by having different firmware versions for different versions of the standard.

In addition the Field Device must have an XML device profile for each version of the standard that it supports. To facilitate this the latest WITS Document Pack includes the device profiles files for every released version of the WITS standard. The device profiles for each supported version of the standard should be included with your WITS verified or self-certified application.

For a Master Station to be compatible with Field Devices that only support an older version of the standard the Master Station must also support the same version of the standard as the Field Devices. The Master Station must check the WITS version reported by the Field Device in its group 0 device attributes and then use this version to determine what is supported by the Field Device. For example, the Master Station should generate incremental configuration files (during a configuration download) in the format supported by the Field Device.

In addition the Master Station must have an XML device profile for each version of the standard that it supports. To facilitate this the latest WITS Document Pack includes the device profiles files for every released version of the WITS standard. The device profiles for each supported version of the standard should be included with your WITS verified or self-certified application.

 

Testing a device

The requirements for WITS device testing are covered in the WITS Compliance Testing Manual, which is made accessible to PSA members along with the Application Notes on joining the PSA.

The WITS Test Specification is available to purchase from the PSA Secretary.

Note that two WITS Master Station vendors offer a “test licence” enabling vendors to use the Master Station software to assist vendors in testing their Field Device (see web site News item – 4-Nov-2014 Test Master Station Software Now Available)

Not at present, but the PSA are willing to explore this if there is sufficient demand.
It is considered as the safest method to ensure interoperability.
Verification gives a greater level of confidence to a potential user.

On Thames for example, the first products underwent full verification but later products may be Self Certified now that confidence has been established with the client user.

The product can be Self certified to Ver 1.3 and still Verified to ver 1.2 without going through the full re-Verification process.

 

Device compliance to the WITS standard

The WITS PSA does not formally verify device compliance, vendors claim accreditation for their device to the PSA and provide evidence to support this claim. The evidence is checked by the PSA ( refer to the “How to achieve self certified and verified status” document for details ) and if accepted, formal recognition given and an entry on the device catalogue area on the WITS website created.
Vendors have a choice of accreditation levels for their device :-

WITS Verified – The vendor must prove product interoperability by testing the Field Device or Master Station against products from a separate development entity to ensure a higher level of assurance.
WITS Self-certified – Tests will be conducted by the vendor themselves using an appropriate test harness / simulator, WITS Field Device or WITS Master Station.
The implications of following these two paths are described in detail in How to achieve self certified and verified status, however, it is recommended that new products wishing to claim WITS-DNP3 compliance follow the Verified status route.

1.3 products must support 1.2, therefore 1.3 Master Stations can be used to test 1.2 products.

However, Field devices must be 1.3 compliant

The device profile (which is available to all on the website) shows which features have been included for a particular product.

 

Registering a device

Device ‘registration’ is effectively the appearance of a vendors device in the WITS device catalogue. This happens automatically during the process of a successful accreditation claim / request as described in the document 150327 How to achieve WITS Certified Status inc Device name strings
For a Field Device, the signatures of the 2 master Station vendors plus the Field device manufacturer are required on the form.
For a Master Station, the signatures of the three Field Device vendors plus the Master Station vendor.

 

About the PSA

The PSA’s Role

The PSA are the guardians of the Water Industry Telemetry Standard (WITS) protocol, and our role is to provide long term maintenance and management of WITS, and to bring governance to its ongoing development.

 

PSA Membership

Membership of the PSA will enable your organisation to gain access to the full Application Notes and other technical documentation necessary to development WITW protocol and to achieve WITS-DNP3 certified status with its associated benefits.

  • Access to Application Notes
  • Access to Compliance Testing Manual
  • Access to Device Profiles
  • Access to members only sections of website
  • Access to listing of certified products
  • Use of WITS-DNP3 logo on certified products
  • Election and nomination rights to the Protocol Standards Association Committee
  • Voting rights at Meetings
  • Product features on website
  • Hyperlink to member’s website
Click on the “Join now” tab

Download a Corporate Membership form by clicking on the link on the page Complete and sign it Send it to the WITS PSA Secretary at the address on the form with your cheque

or

scan and email it to enquiries@witsprotocol.org if you prefer to pay by bank transfer (bank details are on the form). The applicant will then be registered as a Member on the website.

Individuals can only join if they belong to a currently registered Member organisation.

For additional persons from your organisation who wish to become Members and access the Members-only pages, download an Additional Membership form from the “Join now” page, complete and sign it and scan/email or post it to the WITS PSA Secretary. There is no fee for additional members.

 

The PSA Committee

The Committee has responsibility for the overseeing of the maintenance, development, documentation, guidance to achieving self-certified or verified status and promotion of the Standard on behalf of the UK Water Industry.

See the PSA Constitution for more details.[wpdm_file id=9]

See the current Committee list here