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Absolute pressure
Pabs is the pressure compared to a perfect vacuum.

The closeness of a reading of a measurement device to the actual value. Usually expressed as ± percent of Full-Scale (FS) output or reading (Rd).

Actual flow
Flow rate expressed in amount of fluid per unit of time. This in contrast to percentual flow rate. Actual and percentual flow are user-selectable display options at Bronkhorst's readout/control devices (Bright/E-7000/E-8000)

Ambient conditions
Temperature and pressure conditions around the measuring device.

Attitude sensitivity
The accuracy error caused by mounting an instrument under a certain angle (max. error at 90° off horizontal).

"As found" calibration
Calibration is performed with the instrument before any adjustments are made.

"As left" calibration
The instrument has been adjusted and the calibration is being performed with the adjustments.


Back pressure control
Control of the pressure at the outlet side of the pressure controller.

Baud rate
Data transmission speed of instruments connected to a fieldbus.

Most of Bronkhorst's thermal mass flow meters/controllers operate on a principle where the gas flow is split in two, leading a small part through a sensor channel and the remainder through the parallel main channel, in a constant ratio. Due to a perfect 'flow split' the sensor indicates a highly accurate measuring value over the entire range of the instrument.


Adjusting an instrument so that its reading can be correlated to the actual value being measured.

hemical Vapor Deposition. Chemical process whereby a gas flow reacts and deposits a thin, high purity film on a substrate, e.g. a silicon wafer, but also used for surface hardening and production of synthetic diamonds. 

ontrolled Evaporator Mixer. Bronkhorst's vapour delivery system, consisting of a liquid flow meter with control valve, a carrier gas flow controller and a mixing chamber with temperature control.

Coriolis principle
Direct mass flow measuring principle based on the 'Coriolis effect'. The Coriolis forces in a vibrating tube cause changes in frequency, phase shift or amplitude. The output signal of the sensor is proportional to the mass flow.


Differential pressure (ΔP)
Pressure difference between two locations in a system, for instance between the inlet and outlet of a measuring device or control valve, or the ΔP between two fluid lines or vessels.


lectroMagnetic Compatibility. All electronic devices manufactured by Bronkhorst® are complient to EC directive 2004/108/EC. Please find here our Certificates and Declarations.

lectronic Pressure Transducer (also called Pressure Meter).

lectronic Pressure Controller. Pressure meter with integrated control valve.


Forward pressure control
Control of the pressure at the inlet side of the pressure controller.

FS = Full Scale
Closeness to actual value expressed as percentage of maximum scale value. See: ± percentage of Full-Scale (FS) vs percentage of Reading (Rd)


Gauge pressure
The pressure difference between the system and the surrounding atmosphere.

igh Pressure Liquid Chromatography. A commonly used analytical method to verify the exact amount of chemical compounds in a fluid sample.


Ingress Protection class. Protection against solid particles larger than 1 mm, but no protection against moisture.

Ingress protection class "weatherproof". Dust tight, protected against water jets.




Laminar Flow Element
Flow obstruction in the main channel of a thermal mass flow meter/controller. Due to the created pressure difference a proportional part of the flow is lead through the sensor channel, in parallel to the main channel.

Load impedance
The impedance presented to the electrical connector of an instrument.

Low Voltage Directive. European directvie 2006/95/EC, relating to electrical equipment designed for use within certain voltage limits, is applicable to Bronkhorst® Power Supply devices. See our Certificates and Declarations.


Base block on which a variety of functional modules for gas flow, liquid flow or pressure measurement/control as well as filters and mixing chambers can be mounted or integrated.

Quantity of substance expressed in (kilo)gram.

Mass Flow Controller. Combination of a mass flow meter with a control valve for control of gas or liquid flows.

Mass Flow Meter. Flow meter measuring mass flow, in contrast to volumetric flow.


Each individual system component in a bus system.



Percentual flow
Flow expressed in percentage of the full scale value. This in contrast to actual flow.



Rangeability / Turndown
The percentual range (e.g. 2...100%) or the ratio maximum:minimum measuring value (50:1) in which the specified accuracy is achieved.

Rd = Reading
Closeness to actual value expressed as percentage of the actual value. See: ± percentage of Full-Scale (FS) vs percentage of Reading (Rd)

The variability span for the measuring value when measurements are consecutively repeated under the same conditions.

Response time
Time required for the output of a measuring device to change from its previous state to a final settled value within a tolerance band of the correct new value.

Restriction of Hazardous Substances. Directive 2002/95/EC on the restriction of the use of certain hazardous substances in electrical and electronic equipment. See our Certificates and Declarations.


Settling time
The time required for a (flow or pressure) controller to settle and remain at a given value once an input signal is received.

Specific heat / Specific heat capacity / Heat capacity (Cp)
The amount of heat needed to raise an amount of substance (mass) by a certain temperature, expressed in J/(kg·K). Cp refers to constant pressure. 

Surface Mount / Top-mount
Mounting of an instrument on the surface of a base block (e.g. a manifold), due to which the tubing need not be dismounted in case of inspection or exchange of the device.


Thermal principle
Measuring principle whereby flowing gas/liquid (partially) gets heated, resulting in a temperature difference (ΔT) picked up by two temperature sensors. This ΔT is proportional to the mass flow. This principle is based on heat transfer and therefore dependent of the density and specific heat of the fluid. Therefore thermal mass flow meters/controllers need to be calibrated for a specific fluid. The effect of pressure or temperature changes is relatively small, compared to volumetric flow measurement, however for optimum accuracy it cannot be neglected. Conversion factors or additional calibration curves may be helpful in this case.

Top-mount / Surface Mount
Mounting of an instrument on the surface of a base block (e.g. a manifold), due to which the tubing need not be dismounted in case of inspection or exchange of the device.



Volumetric flow
Flow expressed in volume units per time units. The only flow meter technology that measures volume directly is the positive displacement flow meter.





Zero drift
Offset from the true zero. Slow and usually non-periodic change of the zero point of a measuring instrument.