The invention provides a real time process control system for control of machinery. The system has a master control module and a slave control module which receives control signals from the master control module. Both control modules send control signals to a control effector and cause changes in at least one effect causing quality of the control effector. The slave control module establishes a target value for the effect causing quality of the control effector based on the signal it receives from the master microprocessor. A sensor connected to the control effector and to the slave control module provides signals in the slave control module which indicate an actual value for the effect causing quality of the control effector. A feedback loop controls the control signal from the slave microprocessor to the control effector to adjust the value of its effect causing quality in accordance with the target value. In the event that the signal from the master control module to the slave control module is interrupted a discrepancy between actual and target values of the effect causing quality indicates interruption of the signal. The invention provides an increased deadband for the feedback loop to permit a discrepancy large enough to be detectable and useable as an indication of interruption of the signal from the master control module to the slave control module.