Flow

Paddlewheel and Positive Displacement (PD) Flow Transmitters: Paddlewheel devices have a paddle wheel mounted perpendicular to the flow path, and are used determine the flow, in an enclosed pipe, of gas, air, and liquids. PD devices measure the volume or flow rate of a moving fluid or gas by dividing the fluid or gas into fixed, metered volumes or parcels. These devices have a rotating or reciprocating mechanism that allows passage of these parcels. The number of parcels that pass through the chamber determines volume. The rate of revolution or reciprocation determines the flow rate.

Things to Consider: Display specifications, Ambient temperatures for operation and storage, Relative humidity range requirement, Protection class (NEMA 4 IP65 or IP20), Standard (CE), Approvals by UL and/or CSA, Transmitter materials, Electrical connections, Pipe diameter, Measuring range (feet/second or meters/second), Maximum temperature of medium, Maximum fluid pressure, Maximum viscosity, Maximum solid particles content, Accuracy, Linearity, Repeatability, Power supply options, Battery type, Current consumption with and without relay, Output signal specifications, Installation position, Fluid fittings specifications, Dimensions, Warranty.

Magmeter Flow Transmitter. A device with no moving parts that measures the volumetric flow a fluid, and converts that measurement to an electrical signal that can be used to operate an integrated digital or analog readout, or to control another device. Because the measurement is based upon Faraday’s Law, which involves ratio between the velocity of a conductor through a magnetic field and the voltage generated, the fluid being measured must be electrically conductive. There are two common types of magmeter transmitters: insertion and in-line.

Things to Consider: Flow rate range and units; Accuracy; Meter output choices: Indicate, Totalize, Record, Transmit, Compute, Other; Enclosure choices: Wall mount, Panel mount, NEMA code; Piping considerations: New, Existing, Elevation, Straight pipe run, accessibility, Environment; Meter servicing organization for troubleshooting and calibration; Service life; Acceptable value for pressure drop through the meter; Budget; Media to be metered; Pressure min/max; Termperature min/max; Viscosity min/max; Pipe size schedule and inside diameter (ID); Max distance of electronics unit from sensor is 500 feet, Fitting types needed to insert into process, Wetted parts materials and chemical compatibility with media, Housing materials, Sensor and electronics unit dimensions/weight, Electrical power requirements, Contoller to sensor cable length, Minimum conductivity of media required for proper operation (typically 20 microSiemens), Outputs in current and voltage values, Frequency of pulses per unit volume, High and low alarms, Relay, Hysteresis, Low flow cutoff, Warranty.

Orifice Flow Transmitter. A device that measures the flow rate of liquids or gases, and converts that measurement to an electrical signal that can be used to operate an integrated digital or analog readout, or to control another device. The flow is measured through the differences in pressure from the upstream side to the downstream side of an obstruction (the orifice) that narrows flow path and causes the liquid or gas to constrict. The greater the flow, the greater the difference in pressure.

Things to Consider: Flow rate range and units; Accuracy; Meter output choices: Indicate, Totalize, Record, Transmit, Compute, Other; Enclosure choices: Wall mount, Panel mount, NEMA code; Piping considerations: New, Existing, Elevation, Straight pipe run, accessibility, Environment; Meter servicing organization for troubleshooting and calibration; Service life; Acceptable value for pressure drop through the meter; Budget; Media to be metered; Pressure min/max; Termperature min/max; Viscosity min/max; Pipe size schedule and inside diameter (ID); Max distance of electronics unit from sensor is 500 feet, Fitting types needed to insert into process, Sensor and electronics unit dimensions/weight, Electrical power requirements, Warranty.

Rotameter. A device that measures the flow rate of liquid or gas in a closed tube. It is a variable area meter, which measures flow rate by allowing the cross sectional area that the fluid travels through to vary. A rotameter consists of a tapered glass tube with a float inside that is pushed up by flow and pulled down by gravity. At a higher flow rate more area is needed between the float and the tube to accommodate the flow, so the float rises. The float is shaped so that it rotates axially as the fluid passes, allowing one to tell if the float is stuck since it will only rotate if it is free. Readings are usually taken from the top of the float.

Things to Consider: Maximum flow, Units, Standard Accuracy, Repeatibility, Useful flow range, Maximum operating pressure, Maximum operating temperature, Flow tubes material, Floats material, Choice of mounting fittings in contact with fluids, Side panels material, Front shield material, Magnifier lens, Back plate material, O-rings and packing materials, Inlet and outlet connection specifications, Leak integrity, Chemical compatibility of materials with media, Dimensions, Warranty.

Flow Switch: A device that monitors flow and sends an electronic signal to another device such as a pump to protect or control it. Flow switches are used for pump protection, cooling circuit protection, flow-rate alarms, and general flow monitoring. Flow switches are available for use with air, steam or liquid.

Things to Consider: Relay switch type and power requirements, Nominal sensitivity (% flow change needed to activate switch), Pressure drop, Maximum pressure and temperature, Minimum temperature, Wetted parts materials chemical compatibility with media, Electrical cable diameter needed for water resistance when used with electrical cable fitting on flow switch, Flow range, Switch point adjustment range, Pipe sizes accomodated, Weight, Dimensions, Warranty.

Differential Pressure Switch. A device which uses differential air pressure to actuate an electric switch at a pre-set actuation point. This may be the difference between two positive or two negative pressures, one of each, or a positive and atmospheric or a negative and atmospheric pressure.

Things to Consider: Storage temperature, Ambient temperature, Maximum media temperature, Shock (MIL-STD-810), Vibration (MIL-STD-810), Enclosure classification, Set point repeatability, Switch output, Electrical rating, Weight, Electrical connection, Mounting and installation requirements, Listings and certifications, Warranty.

Gas Flow Transmitters/Controllers. These devices measure gas flow in pipes or ducts ranging from _ in tubing to flue stacks greater than 25 ft in diameter, and generates an electrical signal that can be used to control a readout, controller component, or other device. Usually ultrasonic in design, they are obstructionless, cause no pressure drops, and require little maintenance. Analog and digital outputs in velocity and actual volumetric flow rate are standard.

Things to Consider: Typical accuracy, Calibratable accuracy, Repeatability, Rangeability/turndown, Gas temperature, Flow range, Flow sensitivity, Data refresh rate, Minimum pressure, Pipe size range, Display, RTD temperature sensor, Outputs, Analog inputs, Programmability, Optional outputs, Status/Alarm/IO features, Data logger memory size and programmable functions, NEMA rating, Weight, Dimensions, Power, Warranty.