Bronkhorst RS232 interface - Manual (Page 27)

BRONKHORST ®
Page 27 RS232 interface 9.17.027
4 DUAL INTERFACE OPERATION
When operating a controller (reading measured value and sending setpoint) for proper operation it is important that
the controller gets its setpoint from the right source. Setpoints may come from different sources: analog input, field
bus interface or RS232 or may be overruled by close valve or open valve (purge) commands. Therefore it is important
to know what the setpoint source of the controller is. This can be set by means of parameter control mode (process 1,
parameter 4).
In some cases it is possible that the setpoints may come from 2 sources at the same time. The last send setpoint will
be valid and send to the controller. This is the case in control mode = 0, when setpoints may come through any field
bus interface or RS232.
However, there could be situations where control over the instrument seems impossible. This is the case when the
instrument comes into a safe‐state e.g. when field bus communication is disturbed or disconnected. Valve will be
forced to a safe state automatically: closed (NC) or fully open (NO).
In case you want to get control back via RS232 operation, you have to change the control mode. When control mode
gets value 18, safe state will be overruled and sending setpoints via RS232 interface will have effect on the controller
again.
See also document nr. 9.17.023 for more detailed description about digital instrument parameters and
their behaviour.
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