In this section you can find an alphabetical list of terms, abbreviations, and acronyms used across flow and pressure measurement and control equipment as manufactured by Bronkhorst.

Choose a letter below to navigate directly to your selection, or alternatively scroll down to browse the list.

Absolute pressurePABS is the pressure compared to a perfect vacuum.
AccuracyThe 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 flowFlow 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 conditionsTemperature and pressure conditions around the measuring device.
"As found" calibrationCalibration is performed with the instrument before any adjustments are made.
"As left" calibrationThe instrument has been adjusted and the calibration is being performed with the adjustments.
Attitude sensitivityThe accuracy error caused by mounting an instrument under a certain angle (max. error at 90° off horizontal).
AdjustmentWith adjustment of the measuring signal we mean that we change the settings of the meter according to the values of the used reference device. This to eliminate systematic measurement deviations.
Back pressure controlControl of the pressure at the inlet side (P1) of the pressure controller. A back pressure controller is situated at the downstream side of a process.
Baud rateData transmission speed of instruments connected to a fieldbus.
BypassMost 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.
CalibrationCalibration is comparing the output of a measuring device with a reference.
CEMControlled 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. Read more.
CIPCleaning In Place. Method of cleaning the interior surfaces of pipes, vessels, equipment, filters, and fittings. A typical CIP cycle consists of various steps including washing with a hot cleaning agent and hot acid with temperatures up to 95°C.
Coriolis principleDirect 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. Read more.
CVDChemical 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.
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.
Downstream pressureSynonym of Outlet pressure or P2, the pressure at the outlet of an instrument.
EMCElectro Magnetic Compatibility. All electronic devices manufactured by Bronkhorst® are complient to EC directive 2004/108/EC. Please find here our Certificates and Declarations.
EPCElectronic Pressure Controller. Pressure meter with integrated control valve.
EPTElectronic Pressure Transducer (also called Pressure Meter).
Forward pressure controlControl of the pressure at the outlet side (P2) of the pressure controller. A forward pressure controller is situated at the upstream side of a process.
FS = Full ScaleCloseness to actual value expressed as percentage of maximum scale value. See: ± percentage of Full-Scale (FS) vs percentage of Reading (Rd)
Gauge pressureThe pressure difference between the system and the surrounding atmosphere.
HPLCHigh Pressure Liquid Chromatography. A commonly used analytical method to verify the exact amount of chemical compounds in a fluid sample.
IP40Ingress Protection class. Protection against solid particles larger than 1 mm, but no protection against moisture. Read more
IP65Ingress protection class "weatherproof". Dust tight, protected against water jets. Read more
Laminar Flow ElementFlow 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 impedanceThe impedance presented to the electrical connector of an instrument.
LVDLow 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.
ManifoldBase 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.
MassQuantity of substance expressed in (kilo)gram.
MEMSMicro Electro Mechanical System (MEMS) is a technology that in its most general form can be defined as miniaturized mechanical and electro-mechanical elements (i.e., devices and structures) that are made using the techniques of microfabrication.
MFCMass Flow Controller. Combination of a mass flow meter with a control valve for control of gas or liquid flows.
MFMMass Flow Meter. Flow meter measuring mass flow, in contrast to volumetric flow.
MTBFMean Time Between Failures. The predicted elapsed time between inherent failures of a device/system during operation.
NodeEach individual system component in a bus system.
Nominal flowWhen 'Nominal flow' is indicated for a liquid flow meter, this refers to flow rate at which water at reference conditions – typical 1 bar(g) and 20 ºC – causes approx. 1 bar(d) of pressure drop across the instrument.
Percentual flowFlow expressed in percentage of the full scale value. This in contrast to actual flow.
PID controlPID control stands for Proportional–Integral–Derivative control. PID control is a feedback mechanism used in a control system. In the case of our flow controllers, it directs the control valve to open or close to maintain a constant flow at the set point. 
ProParShort for 'Process Parameter', the Bronkhorst specific parameter model for RS232 and FLOW-BUS communication.
Rangeability / TurndownThe percentual range (e.g. 2...100%) or the ratio maximum:minimum measuring value (50:1) in which the specified accuracy is achieved.
Rd = ReadingCloseness to actual value expressed as percentage of the actual value. See: ± percentage of Full-Scale (FS) vs percentage of Reading (Rd)
RepeatabilityThe variability span for the measuring value when measurements are consecutively repeated under the same conditions.
Response timeTime 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.
RoHSRestriction 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 timeThe 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.
Specification limit The specification limit is the maximum allowed  value (error limit) of a measurement deviation; this can be both a positive or negative deviation. This term is used, for example, in the context of calibrations.
Surface Mount / Top-mountMounting 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 principleMeasuring 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. Read more
Top-mount / Surface MountMounting 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.
Time ConstantThe time constant can be defined as the time it takes for the measured value to reach 63% of its final value after a change of setpoint.
Turndown ratio

Turndown ratio is also commonly referred to as rangeability. It indicates the range in which a flow meter or controller can accurately measure the fluid. In other words, it's simply the high end of a measurement range compared to the low end, expressed in a ratio and is calculated using a simple formula:

Turndown ratio = maximum flow / minimum flow

Ultrasonic principleThe basic principle of ultrasonic flow meters is the transmition of a sound(s) wave(s) through a pressured liquid into a pipe. The distinctive character of Bronkhorst's ES-FLOW flowmeter is that it’s capable to measure the actual speed of sound, meaning that the technology is liquid independent and calibration per fluid is not necessary, contrary to other (traditional) ultrasonic flow measuring principles based on the transit time or the Doppler effect. Read more.
Upstream pressureSynonym of Inlet pressure or P1, the pressure at the inlet of an instrument.
VDMA VDM - Vapour Delivery Module - is an all-in-one evaporation device, incorporating gas and liquid flow controllers, a temperature controlled evaporator and a display with control functions to readout and adjust the gas flow, the liquid flow and the temperature of the mixture that exits the VDM as a homogeneous vapour. Read more.
Volumetric flowFlow expressed in volume units per time units. The only flow meter technology that measures volume directly is the positive displacement flow meter.
Zero driftOffset from the true zero. Slow and usually non-periodic change of the zero point of a measuring instrument.