Water Industry Telemetry Standard (WITS) is a communications protocol designed for use within the water utility industry between components of a SCADA system. It was developed for communications between a WITS Master Station and its remotely connected WITS Field Devices (for example, Remote Telemetry Units).
WITS is based on the DNP3 protocol level2+, and uses DNP3’s generic protocol extension mechanism to define and provide the additional functionality required by water industry users. While initially developed by and for the Water Industry, the WITS protocol is a generic SCADA Communications protocol.
The WITS functionality was originally defined in the mid 2000s by the UK water companies via a joint UK Water Industry / equipment vendor’s team. During 2011, ownership of the WITS protocol passed into the hands of the WITS Protocol Standards Association for future management and maintenance.
WITS adds functionality to the underlying DNP3 protocol :-
Device Profiles
The characteristics and capabilities of a particular WITS Field Device are defined in a ‘device profile’, which is in XML format. This 'device profile' is read into the WITS Master Station and used to limit what a user can do to that particular Field Device.
Device Configuration
WITS provides Master Stations with the ability to incrementally change the configuration of Field Devices. This is done by using DNP3 file transfer to send incremental configuration updates to a Field Device. This mechanism provides flexibility for managing the configuration of remote Field Devices from a central location. Examples of configuration changes could be analog input scaling, definition of alarm limits and enabling / disabling inputs.
Information exchange between a WITS Master Station and Field Device
WITS defines seven DNP3 'Data Sets' for Field Devices to report data to a Master Station and for a Master Station to control a Field Device. These are as follows :-
for reporting data - change of state or transgression of a limit
for monitoring the health of a device
for requesting a device to 'call in' and test a communications path
for controlling programs sent to a Field Device
for controlling whether inputs cause events to be sent to the Master Station
Data Logging
WITS Field Devices can record local data log files. These contain data with a time stamp and retrieved later by a Master Station. The logs are retrieved by means of DNP3 file transfer.
WITS devices are 'accredited' in one of two forms:
WITS Self certified
Tests have been conducted by the vendor themselves using their own test equipment.
Tests did not involve any third party.
The tests demonstrate compliance with either the WITS PSA Test Specification, or the vendors own test specification.
WITS Verified
Tests have been carried out using WITS verified equipment in conjunction with one or more third parties who can provide WITS Verified devices for testing.
Verified Outstations have been tested against two verified WITS Masterstations
Verified WITS Master stations have been tested against three WITS verified field devices
Testing has confirmed compliance with the WITS PSA Test Specification.
