PROFIsafe as an enabling technology has been initiating new possibilities for standard and safety devices. This chapter is to provide a brief overview on some important F-Devices and typical applications.
Standard remote I/O now are able to incorporate safety modules without changing the head stations. F-Modules such as digital input/output, analog input/output, power modules, motor starter, and frequency converters with integrated safety are available. The F-Modules can be grouped together and allow shut-down in groups.
Emergency stop buttons need very costly yearly inspections as each and every button has to be tested. The new technology allows for easy collection of all actuations over the year. This way only the remaining unactuated buttons have to be tested, thus saving tremendous costs.
Optical safety sensors such as light curtains and laser scanners are standardized within IEC 61496. Optical sensors are ideally suited to protect entry/exit portals in a flexible manner. The example in Figure 18 also shows how PROFIsafe complements the safety features of laser scanners and drives with integrated safety. See details below.
The safety features of drives are standardized in IEC 61800-5-2. These safety functions usually require a safe position indicator. The value is available to the user via PROFIsafe and can replace physical "end-of-travel"-switches or physical "muting"-sensors. As shown in Figure 18 the motor position affects the protection fields of laser scanners according to the profiles of car bodies at entry/exit portals of a manufacturing cell.
Safety features for robots can be found in ISO 10218. The new safety features for drives foster robots to integrate those features and provide new functionality such as "collaborative robots", where persons work hand-in-hand with robots.
For PROFIsafe an F-Gateway to AS-i Safety-at-work (ASIsafe) exists. This device combines the advantages of both worlds. While ASIsafe can easily collect the signals from many emergency stop buttons connected in series, PROFIsafe is easily able to deal with sophisticated F-Devices such as drives with integrated safety.
It was already mentioned that safety for process automation follows its own sector standard IEC 61511. NAMUR, as standards body for chemical and pharmaceutial industries publishes the companion standard NE97 specifying how safety communication can be used with safety field devices. A "proven-in-use" PA Device, equipped with a PROFIBUS MBP-IS interface, accommodates a PROFIsafe driver that can be configured "Off" or "On". In one mode it represents a standard PA Device, in the other mode an F-Device (Figure 2).
NAMUR initiated another companion standard, the VDI 2180, which facilitates the development of safety-related PA Devices.
Currently most of the PROFIsafe applications in process automation deploy remote I/O with F-Modules for 4-20mA or HART communication. Figure 3 demonstrates the two possibilities for using PROFIsafe with "proven-in-use" PA Devices. This is a good compromise even though it suffers from the lack of the direct fieldbus advantages such as wide range measurements, parameterization and sophisticated diagnosis.
- Level switches
Level switches for tanks benefit much from the PROFIsafe technology. PROFIBUS PA with its MBP-IS and RS485-IS explosion-proof transmission technologies fit well into the requirements of these F-Devices. PROFIsafe provides the safety transmission of the shut-down signals while the standard "black channel" informs the user about the status of the sensors.
- ESD valves
Similar improvements can be achieved for ESD (Electronic Shut-Down) valves. The main objective here is to periodically test the valve function through "partial valve strokes" and trend monitoring of the end position and of the time elapsed to reach this position. This can be done automatically via F-Hosts and allows predictive maintenance whenever it is convenient for the user. The RS485-IS communication together with barriers allows fast shut-down even within an Ex-i environment.
- Press transmitter
Safe pressure transmitters combine the function of measuring the tank filling and of protection against overflow ("level switch") via comparison with a setpoint value.
- Gas and fire sensors
These sensors are in service on unmanned oil platforms for example. Additional position information makes it possible to automatically batten down the relevant hatches.