7000 series products include a rugged, cleanable, thermal mass flow sensor. These units consist of a sensor assembly which utilizes two RTD (Resistance Temperature Detector) sensing elements. The sensors are constructed of reference grade platinum, ceramic, glass, and stainless steel. Two platinum resistance sensors are built up upon the ceramic substrate and then given a thin glass coating. The assembly is then slipped into a stainless-steel sheath for corrosion and abrasion resistance. The sensor assembly is large, rugged, and relatively insensitive to dirt buildup. During operation, the temperature sensor constantly measures the ambient temperature of the gas and maintains a reference resistance on one side of a bridge circuit. The second sensor is forced through self-heating to a constant temperature above that of the gas stream and is controlled by the temperature sensor and bridge circuitry. Our bridge maintains the overheat temperature and counterbalances the temperature effects through our proprietary temperature compensation techniques.

7000 Series flow switches have not been submitted for agency approval testing.

The Inline style thermal mass flow switch assembly includes the flow sensing element, temperature sensing element, bridge amplifier/signal output board, transmitter enclo­sure, and flow section. The flow section is typically specified to match the user’s flow conduit and is plumbed directly in the flow line. This design has the sensing elements mounted directly in the flow section for exposure to the process flow.

Inline flow switches are available in sizes from 1/4″ pipe through 4″ pipe and are provided with threaded male NPT ends as the standard mounting style. Optional end mounting styles may be specified, such as tube ends, tube end fittings, butt weld ends, flanged end configurations, etc. as required. Pipe sizes more than 4″ require insertion style thermal mass flow switches.

All of EPI’s flow switches have two single-pole, double-throw relays for Hi/Hi, Lo/Lo and Hi/Lo capability. The contact closure is 5 amps @ 24 VDC and 115 VAC. Two LEDs are provided for verification that the Hi or Lo alarm has been triggered. The standard configuration has 316 Stainless Steel wetted parts (Hastelloy & Monel are also available) for a rugged, cleanable instrument designed for use in applications where corrosion, abrasion, high pressure, or rough handling may be expected.

Thermal mass flow switches use the principle of convective heat transfer to directly measure mass flow. EPI’s proprietary thermal mass flow sensors use two ratiometrically-matched, reference-grade platinum Resistance Temperature Detectors (RTDs). The platinum sensing element wire is encapsulated in a 316 Stainless Steel sheath or, if specified, a Hastelloy C sheath. Our microcontroller operated smart sensor technology preferentially heats one RTD; the other RTD acts as the temperature reference. The process gas flow dissipates heat from the first RTD, causing an increase in the power required to maintain a balance between the RTDs. This increase is directly related to the gas molecular rate of flow. Our sensors are temperature compensated for a wide process gas temperature range and insensitive to pressure changes, so the output signal is a true mass flow rate signal.