Rate meters or rate indicators provide a digital display of a process. The simplest ratemeters connect to a sensor and give a direct readout of frequency or voltage which is representative of rate or speed. Proper choice of a sensor allows the indicator to show process variables in engineering units such as motor revolutions/minute or material feet/minute. Some rate meters have calibration which scales, or converts, the input signal to engineering units with almost any sensor choice. Applications where the sensor cannot be easily specified for direct readout or unusual measurements may need calibration.
Rate controllers add the ability to monitor and compare the input to one or more values. These values are typically called “alarms” in rate control applications. In addition to the operator display, the “alarms” can trigger control outputs or relays to prevent out-of-tolerance operations or take corrective action to bring the process within its normal limits. In many applications, out-of-tolerance conditions are indicated by visual alarms.