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 maximum pressure of gas that can be safely flowed through the device.
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 highest pressure at which the device can flow and perform measurements.
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