Tips for Reading a WITS Device Profile
The WITS-DNP3 Protocol is an open communications protocol designed to allow Field Devices to talk to Master Stations within the water industry. For the first time the protocol gives the water industry a common language for communication between devices in the field and their telemetry masters. In turn this provides the users with a genuine choice of Field Device instead of being tied into using the Field Devices made by the vendor of the Master Station they have deployed.
Having been given that choice, the users now need a method of determining which Field Device to select for any particular project. Each project may have its own requirements, for instance:
- A specific communications medium to be used. Maybe the outstations deployed for the project are to be battery powered and should support TCP communications over GPRS.
- A specific regime for recording data at the device. For example, in CSO monitoring it may be necessary to keep records of the 15 minute values of sewage level against the weir. In the case of WITS this is called “logging”.
- A specific alarming regime. The device may need to monitor its inputs and when they exceed certain levels, either log those values or make them immediately available to the Master Station.
The user must now match the project requirements against the capabilities of the WITS Field Device to ensure that the device is capable of meeting all the requirements. The WITS Device Profile is a good starting point for users to do this. It also assists users in comparing devices, and, more fundamentally to the WITS-DNP3 Protocol, permits the Master Stations to understand the capabilities of a device in an automated manner. However, to support this function with the Master Station, the WITS Device Profile in its base form is presented as an XML document, which tends not to be easy for users to read. More user-friendly forms are available and these will be discussed later.
This article seeks to demystify the WITS Device Profile for users by: explaining what the Device Profile is, how it can be acquired, what forms it takes, how to read simple setting from the profile, and various issues to be aware of when reading the Device Profile. The article is suitable for users of the WITS-DNP3 Protocol and may also be of use to new vendors hoping to gain an understanding of the WITS Device Profile. Within this article we also use the term “Device Profile” to mean WITS Device Profile.
What is a Device Profile?
The WITS-DNP3 Protocol describes many different capabilities that a WITS Field Device or Master Station may have. Not all Field Devices or Master Stations implement all of these capabilities. For example, it is possible for Field Devices to support the downloading and running of applications on the device, such as IEC61131-3 applications. However, a battery device designed for monitoring a few signals may not need this level of complexity and may therefore not support it. The Device Profile lists all of the capabilities and describes, for a single device, which capabilities are implemented and which are not.
Every Master Station or Device should have a WITS Device Profile. Indeed, for any device which has self-certification or verification it is a pre-requisite that a Device Profile must be available for that device. Every Device Profile applies to only one device or family of devices.
To deploy a Field Device against a Master Station, the Master Station must have access to a copy of the device’s Device Profile. The Master Station uses this Device Profile to understand what the device is capable of and thereby restricts what the user of the Master Station can do in configuring the device and how the Master Station interacts with the device.
The Configuration Application (CA) for a specific Field Device is the software provided by the device vendor which enables the device to be configured, as discussed in the WITS Application Notes. The CA is capable of providing the correct Device Profile for a device. That Device Profile can then be used by the Master Station.
The Device Profile provides the capabilities of the device and not the specific configuration of the device. The specific configuration of the device is described in the Bulk Configuration File (BCF) and the Incremental Configuration (IC) as laid out in the WITS Application Notes. Note that the BCF and IC must not implement configurations which are not supported by the capabilities laid out in the Device Profile. So, for example, if a Device Profile indicates that the device does not support Rate of Change, then the BCF and IC for that device should not configure that.
As a user, the most important thing the device profile provides is the list of what a device is capable of, allowing a comparison of the devices capabilities against those required to fulfil a specific application. So for example, if a device which is capable of supporting GPRS is required then the communications part of the device profile for the device in question should be checked to see that the device does indeed support GPRS.
Where can I get the device profile?
Device profiles are normally freely accessible from the WITS website or the device vendor. On the WITS website navigate to the Device Catalogue under the Certification tab. The device catalogue lists self-certified and verified devices with links to the vendor’s web sites, their product pages and to the device profiles submitted to WITS for certification. You can see an example of what this looks like below.
Figure 1 – An example of the WITS website Device Catalogue page for WITS verified devices in June 2016. This example shows the Link to Device column which contains version numbers which are hyperlinked to a page which is tailored for each device.
By clicking on the version number in the “Link to Device Profile” column, a page specific to that device and manufacturer is shown, which includes links to display the device profile and to download the device profile. See the screenshot below.
Note that in general the WITS website only carries the device profiles submitted by vendors when they apply for self-certification of verification. This version of the device profile may be older than the current version available from the vendor, so if