Keypad, laptop or host PC? It's down to the application
Mark Daniels looks at the options for programming and configuring drives,
comparing the simplicity and convenience of the built-in keypad with
software based solutions
Despite the significant growth in the number of applications for drive
products and the increasing use of integrated control systems based on
communications networks, over 70% of drives supplied by the author's
company are still ordered with a keypad. Keypads are often the favoured
method of programming simple installations, and users quickly get used to
keypad-based programming routines. They can be built into the drive or
supplied as a separate 'plug-in', enabling programs to be downloaded to
other drives of the same manufacture in a multi-drive installation.
So-called 'Smart Start' keypads guide the user through a quick-start
routine, providing prompts when data needs to be entered.
But while they are simple and convenient to use, keypads do have their
disadvantages. If they are removable, they need to be stored in such a
way that they can be quickly retrieved when they are needed. Because they
are unique to each drive family, several different keypads may be
required for a site where there is equipment from several different
manufacturers. Programming procedures differ from one manufacturer to
another, so users may need to re-familiarise themselves with these
(particularly if they are used infrequently) in the event of a breakdown.
Other disadvantages include the physical limitations of the small LCD
screen, which makes programming anything other than the most simple
tasks, somewhat tedious, while the lack of keypad memory makes the
retrieval of different programs for production line changes rather
difficult.
So, how are complex installations, with several drives working in
combination with other control devices over a fieldbus network, more
effectively programmed? Some manufacturers offer bespoke software
packages, running on a laptop or handheld computer, with Windows features
such as drop-down menus, context sensitive help and colour graphics.
So-called 'light' versions are usually supplied free of charge with the
hardware, while the full version is generally offered at relatively low
cost.
Adding a PC interface brings a lot of features to the programming
environment, allowing applications to be integrated with other PC based
programs or Internet links to be integrated into the software to provide
a path for upgrades. Controls can be emulated as analogue devices to
present a familiar user interface or customised view of the drive.
Configuration files can be stored away for reuse or transfer to another
device on the network, while powerful diagnostics enable faults to be
quickly located and logged. A simple serial connection is all that is
needed to effect the uploading and downloading of programs.
These bespoke solutions are fine when you happen to be using a family of
drives from one manufacturer, but a 'full solution' software package will
be required if you seeking a programming tool that is independent of the
drive type or manufacturer. These powerful PC based systems require a
higher level of operator skill and training; they are not vendor specific
but require an open network to provide access to all control elements -
not just the drives - from a central point. The network can be accessed
at any point, either locally or remotely via a modem, to reconfigure
existing machinery or commission a new system.
Network level tools, including Automatic Device Replacement (ADR), which
as available on the DeviceNet fieldbus, enable additional functions to be
brought into play. ADR automatically manages the configuration of a new
device after it has replaced an existing device on the network. It is
particularly useful for plants that run continuously, enabling a drive to
be quickly replaced by a maintenance technician with little or no
specialist programming or configuration knowledge.
Ultimately, the choice of programming option is determined by the drive
application. For individual drives or stand alone equipment, the simple
keypad is fine. In the case of a 'packaged' machine containing drives and
other control devices from a single manufacturer, the proprietary PC
based solution is more appropriate. But for multi-vendor installations,
network based configuration and management systems are the best solution.
Mark Daniels is drives marketing manager at Rockwell Automation