Flow computers, totalizers, and rate indicators integrate the functions of flow and temperature measurement, computation, data acquisition, input / output (I/O) standardization, and closed loop control. They require external sensor inputs and may be used as local rate indicators. Some flow computers, flow totalizers and flow indicators are designed to monitor the flow of liquids. Others are used to monitor the flow of gases or mixed phases such as steam. Flow computers, totalizers and indicators that measure volumetric, velocity, and mass flow rates are commonly available. Volumetric flow rate indicates the amount of measured medium which flows past the sensor. Velocity flow rate is the speed of the medium. Mass flow rate represents the weight or mass of the medium and can be displayed in units such as pounds per minute (lbs/min).
Flow computers, totalizers and indicators carry specifications for both input channels and output channels. The number of inputs, generic inputs, flow sensor inputs, and additional process inputs are common specifications for input channels. The number of inputs equals the total number of signals sent to a controller and includes process variable signals such as temperature, pressure, level and speed. There are three generic inputs for flow computers, totalizers, and indicators: pulse (frequency), analog current, and analog voltage. Flow sensor inputs are received from differential pressure meters, true mass flow meters, and velocity meters. Additional process inputs include density and temperature. For output channels, the number of control outputs and type of electrical outputs are important specifications to consider. Analog voltage, analog current, frequency (pulse) and switch outputs are common with flow computers, totalizers and indicators.
Flow computers, totalizers and indicators differ in terms of display type, local interface, computer interface, features, and mounting configuration. Analog displays, analog front panels, digital displays, and digital front panels are commonly available. Computer interfaces use serial or parallel protocols and may include application software. Alarms, controllers, programmability, recorders, and sanitary ratings are features for flow computers, totalizers and indicators. Products can be mounted on the flow sensor of flow meter itself, or on a panel, wall, rack or DIN rail. Desktop, portable and laboratory-style flow computers, flow totalizers and flow indicators may also be available.