Application Blocks for Safe Analog Processing

In the past, processing analog signals safely using safety relays was as good as impossible. Only the integration of special expansion modules and the availability of customized application blocks has made safe analog processing possible. In a similar procedure to that of the drive environment, configurable safety relays can be used to evaluate sensor information from the analogue process environment. This may relate to process conditions such as fill level, position or speed for example; there's practically no limit to the extended application
options. With analog signals it is also possible to define limit values, threshold values or value ranges, inside which a measured value may move; this is done through the module configuration or by setting parameters in the user block. Reliable monitoring therefore becomes a reality; all values can be evaluated and further processed.

Example: Range monitoring 4 … 20 mA current loop

With range monitoring, the first step is to define the permitted value range. Depending on the selected condition (“greater than” or “less than”), the output for threshold value monitoring is set to “0” if the recorded value exceeds or drops below a range limit.

2 range limits are to be defined in this example:

• I < 3 mA monitors for open circuit and 
• I > 21 mA monitors for input device error

Example: Monitoring the position of a control valve via range monitoring

Control valves in process technology, e.g. to control flow rates, are generally controlled in analog; feedback on the valve position is also analog. Without safe analog processing, until now, only special switches have been able to evaluate position signals from valves. The new technology allows you to set as many valve
positions as you like and to monitor compliance, safety and reliably.