Flow Sensor Terminology

Detection Range

This is the range of flow rate within which a switching point can be set at the amplifier. The setting ranges and the temperature drift differ for various media. If not specified, the medium is water. At the borders of the detection range, the temperature drift of the set-point will be significantly higher.

Working Range

The working range indicates the section of the detection range for which the flow data is specified. At the outer limits of the detection range, this data is reduced.

Nominal Flow

For each sensor, data corresponding to its own nominal flow is measured. This is necessary because response characteristic curves of sensors are non-linear. Consequently the various sensor characteristics depend on the location of the chosen operating point on the curve. As a rule, the nominal flow-point is set in the middle of the portion of the (simple logarithmic representation of the characteristic) curve which appears to be linear. For this operating point, the following values may be defined: switching on and off times, stand by time, hysteresis and temperature response.

Supply Voltage

The supply voltage is the voltage range within which sensors function safely. For direct current supplies it must be ensured that the limits are maintained even including residual ripple.

Current Consumption

The current consumption is the maximum value of the idle current Io which the flow monitor draws without load.

Switching Current

The switching current indicates the maximum continuous current for the switching output of the device. For PNP outputs this value applies to an ambient temperature of 25 °C. At higher temperatures the maximum switching current is reduced. For devices with relays output the value is related to the utility category AC-12 or DC-12 in accordance with EN 60947-5-1.

Switching Voltage

The switching voltage indicates the maximum voltage (including residual ripple) to be switched with the relay output.

Switching Power

The switching power indicates the maximum power to be placed on the output relays.

Ambient Temperature

The ambient temperature indicates the maximum and minimum permissible temperatures for the sensor.

Temperature Medium

The temperature range for which a sensor is rated. Applies to the medium to be monitored.

Temperature Gradient

The change of the medium´s temperature within a defined period of time is called temperature gradient. These flow sensors have a temperature gradient up to 250 K/min. for water. If the change of medium temperature exceeds this value, there will be a malfunction of the flow controller.

Start-up Time

The start-up time is the period of time required by the flow detector to reach a stable state after the operating voltage has been switched on. Prerequisite is that the medium flows at the rated velocity and that the sensor has adapted to the temperature of the medium before switching the supply voltage on. The start-up time is prolonged in a static medium and reduced if the medium flows faster than the rated value.

Reaction Time

The reaction time combines the switch-on and -off time. Switch-on time elapses from the beginning of the flow until the switching point set at the amplifier is reached. Switch-off time characteristic results for the flow sensors at pump shut-down. If the set switching point is close to maximum flow, the time elapsing between the pump shut-down and the indication of the flow decrease is short. If the switching point is close to the static value, the off-transition time will be long.

Compressive Strength

Pressure resistance relates to the sensor casing. Standard models with metal casings will withstand pressures as high as 100 bar. Up to the indicated maximum pressure, the sensor provides a steady signal and the casing suffers no damage.


The protective system indicates the protection of the sensors against penetration of foreign bodies and water according to EN60529


The variable time delay which can be set between 0 and 25 seconds becomes active during flow standstill (drop-out delay). If the medium ceases to flow and the amplifier display indicates this state, the relay contact is actuated only after the set delay. During the delay period the yellow LED lights up together with the red LED.

Cable Break Monitoring

Cable break monitoring shuts off the flow monitor output if no sensor is connected or if the sensor cable has been severed. In case of cable severing, "flow failure" signal is displayed.

Product search

This product search tool allows you to find the most appropriate sensor to suit the application, with selections for medium (liquid, gas, glycol), power supply, flow rate, supply voltage, output type, connection type, temperature range and ATEX category.

Read More »