Spec sheet glossary of terms

Here is a list of the terms found in Alicat spec sheets and their associated definitions. If you have any questions, please contact us via phone, email, or chat.

Sensor (and control) performance

• Max Flow Accuracy at Calibration Conditions: The accuracy of mass flow when gas is flowed at the conditions indicated on the Certificate of Calibration.
• Volumetric Flow Accuracy at Calibration Conditions: The accuracy of volumetric flow when liquid is flowed at the conditions indicated on the Certificate of Calibration.
• High Accuracy Option: The accuracy of the reading when calibrated using the high accuracy option.
• Bidirectional Option: The accuracy of the reading for a bidirectional controller when gas is flowed at the conditions indicated on the Certificate of Calibration.
• Repeatability: The closeness of the reading between two consecutive measurements under identical conditions.
• Flow Measurement Range: The range in which a device can accurately read flow.
• Temperature Sensitivity: The possible deviation of the sensor readings when the gas temperature is different from 25°C.
• Pressure Sensitivity: The possible deviation of the sensor readings when the gas pressure is different from the calibration conditions.
• Operating Temperature Range: The temperatures of gas that can be safely flowed through the device.
• Operating Pressure Full Scale: The highest pressure at which the device can flow and perform measurements.
• Temperature Accuracy: The possible deviation of the device’s temperature reading from the true temperature of the flowed gas.
• Pressure Accuracy Above 1 atm: The possible deviation of the device’s pressure reading from the true pressure of the flowed gas when the pressure is greater than 1 atmosphere.
• Pressure Accuracy Below 1 atm: The possible deviation of the device’s pressure reading from the true pressure of the flowed gas when the pressure is less than 1 atmosphere.
• Barometric Pressure Accuracy: The possible deviation of the internal barometer reading from the true barometric pressure.
• Totalizer Volume Uncertainty: The possible deviation of the device’s totalizer measurement from the true totalized amount; this is in addition to the uncertainty of the flow rate that is accumulated through the duration of totalizing.
• Sensor Response Time: The amount of time required for the sensor to respond to a change at the flow sensor die.
• Typical Indication Response Time: The amount of time required for the device to register and display a change in gas flow rate through the laminar stack (includes averaging effects). Time given as the time constant, Tc.
• Typical Control Response Time: The time associated with a setpoint being issued and the device attaining the desired setpoint. Time is given as the time constant, Tc.
• Time Constant, Tc: The time constant for a system, assuming an exponential function: f(t) = f₀e^-t/Tc. Each successive time constant duration represents the process value f(t) moving 63.2% closer to the final value. 1 Tc = 63.2% of the final value change and 4 Tc = 98.2% of the final value change.
• Typical Warm-Up Time: The amount of time required for the device to become operable after start up.
• Valve Function: The default valve position when the device is not powered.

Mechanical

• Sensor Burst Pressure: The pressure at which the device’s sensor can become damaged.
• Minimum Operating Pressure: The lowest pressure at which the device can flow and perform measurements.
• Maximum Operating Pressure: The maximum pressure of gas that can be safely flowed through the device.
• Ingress Protection: The ingress protection rating. This signifies the degree of protection against solid objects and liquids.
• Humidity Range: The percentage of allowable humidity in the flowed gas.
• Wetted Materials: Materials of the device that are in direct contact with the media flowing through the device.

Communications

• Analog I/O Options: The available analog input and output options that the device can be configured with.
• Digital I/O Options: The available digital input and output options that the device can be configured with.
• Power Requirements: The voltage and amperage requirements to power the device. These are specific to the model being used.
• Electrical Connection Options: The options for physical electrical connectors on the device.
• Battery Life: The estimated time that a battery powered device will operate for with a single charge.
• Digital Data Update Rate: The rate at which digital signals are sent and received by the device.
• Analog Data Update Rate: The rate at which analog signals are sent and received by the device.
• Display Update Rate: The rate at which the device front panel display updates.
• Analog Signal Accuracy: The possible deviation in the analog signal that is sent/received.

Features

• STP Reference Conditions: The default numerical standard temperature and pressure defined for the device. Can be configured by the customer.
• NTP Reference Conditions: The default numerical normal temperature and pressure defined for the device. Can be configured by the customer.
• Gas Select: A device feature that allows the user to select one of the gases stored in the device’s memory. This selection influences the displayed reading.
• COMPOSER: A device feature that allows the user to create up to 20 gas mixtures. These mixtures can contain up to 5 different gases with a 0.01% composition precision.
• Default Flow Measurement Media: Defines the default liquids that can be flowed through an LC or LCS-Series device.
• Alternative Flow Measurement Media: Defines the compatible fluids with viscosities between 0.1-3.0 cP that can be flowed through an LC or LCS-Series device.

Range-specific technical data

• Process Connections: The fittings located on the ports of the device.  These can be configured in multiple ways as requested by the customer.
• Pressure Drop: The difference in total pressure between 2 points. In Alicat devices, this is defined as the drop in pressure between the inlet and outlet ports.

Units

• PSID: Pounds per square inch differential. The difference between the inlet and outlet pressures of the device.
• Hz: A unit of frequency. One Hz represents one cycle per second.
• PSIA: Pounds per square inch absolute. This unit of pressure is measured relative to a full vacuum. Atmospheric pressure at sea level is roughly 14.696 PSIA.
• PSIG: Pounds per square inch gauge. This unit of pressure is measured relative to ambient atmospheric pressure. Ambient air pressure is 0 PSIG.
• atm: A unit of pressure. One atm (or atmosphere) is equal is 14.696 PSIA.
• SCCM: Standard cubic centimeters per minute
• SLPM: Standard liters per minute
• SCFM: Standard cubic feet per minute
• SCFH: Standard cubic feet per hour