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Technical Information



Thermal Mass Flow Meter Installation & Mounting Guidelines

The Master-Touch™ thermal dispersion sensor must be exposed to the flowing gas in the process pipe at a location that provides a uniform and consistent flow profile across the pipe diameter. Each flow meter is calibrated under tightly controlled conditions in our NIST-traceable facility. Our inline style flowmeters are calibrated with the sensors in a fixed position within the provided flow section. Our insertion flowmeters are calibrated near the ISO Point-of-Average-Flow (.243r) positioning in the process line* with a fully-developed flow profile. However, anomalies in the actual flow profile or installations in non-circular ducts may require adjustments to the flow meter’s output signals or readings to achieve the best accuracy. Although changes to the process gas composition, gas temperature, line pressure, etc. can affect the overall accuracy of the flow readings, these effects are often minimal when compared to their effect on other flow measurement technologies.

*Please note that our insertion style Flow Averaging Tube™ design has a flow inlet tube that extends across the pipe or duct diameter, and therefore does not utilize the ISO Point-of-Average-Flow positioning.

The Master-Touch™ firmware supports two methods of in situ flow signal adjustments for superior accuracy:


    • The C-Factor (Menu 811) adjusts the linearized microprocessor output by a uniform percentage of the readings. This simple adjustment should be applied before any futher adjustments.


    • Point-Wise adjustments (Menu 750 PW-Curve Fit) provide greater flexibility by allowing adjustments in increments of 5% of the Full Scale, i.e., 10–15% or 65–70%. It is unlikely that more than two or three adjustments would be needed to achieve the desired results, however we offer the option to apply those adjustments wherever along the Full Scale that you are able to capture the comparative values.


Please consult the factory for additional information on flow meter installation.

Flow Meter Installation Details

Acceptable limits for the process gas temperature and the environmental temperature to which the transmitter electronics may be subjected are listed in the product-specific pages of this site and the appropriate Manual.

We recommend installing the flow meter at a location where the gas is dry or above the dew point temperature. Installations which allow large droplets of water to condense out and to come in contact with the sensing element must be avoided. Applications with large quantities of gas-borne particulates should also be avoided as the sensor may become dirty which could affect the heat loss to the flowing gas and therefore have a negative impact on the overall accuracy of the flow readings. Gas purge options are available, if necessary. Consult the factory for options.

Optimum installation requires sufficient straight run to allow a uniform, non-swirling, fully-developed flow profile within the flow conduit. General guideline for minimum straight run requirements are included in the Manual for each product. Depending upon the specific location details, more or less straight run may be required to produce a satisfactory flow profile. It is best to avoid installations which are immediately downstream of bends, abrupt cross-sectional area increases or decreases, fans, louvers, or other equipment installed in the line. These situations can cause non-uniform flow profiles and swirl which can result in signal errors. Problematic flow profiles require flow conditioning to improve meter performance. Consult the factory for additional information.

Installation of Inline Flow Meters

The inline style flow meter assembly includes the flow sensing element, temperature sensing element, bridge amplifier/signal output board, microprocessor circuit board, transmitter enclosure, and flow section. Depending on the flow section size and/or other requirements, the flow section may include flow conditioning plates.

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 gas. Inline mounting styles are available through EPI™ for line sizes 1/4″ pipe and larger. Consult our factory for flow section end mounting options.

Inline flow meters are calibrated with the flow sensing element mounted in place within the flow section. The sensor should not be removed as the accuracy of the flow signal will be affected. Should it become necessary to remove the sensing element for any reason, the element must be replaced in the same alignment as it was originally positioned.

Consult the factory before disassembling.

Installation of Insertion Flow Meters

The insertion style flow meters include the flow sensing element, temperature sensing element, bridge amplifier/signal output board, microprocessor circuit board, transmitter enclosure, and the probe assembly which supports the sensing elements. This design requires the probe assembly to be inserted into the process gas flow conduit.

Insertion styles are available with 1/2″, 3/4″ or 1″ OD probes. Insertion style flow meters may be installed with properly sized bored-through tube fittings to mount them in place. Tube fittings, with or without mounting flange, are available from the factory as an option. Installing the tube fitting consists of preparing the flow conduit to accept the fitting by first drilling a clearance hole for the transmitter probe assembly, welding it in place, or threading it into the proper size half coupling which has been welded to the flow conduit. The tube length will be determined by EPI™ based upon the installation specifications.

Optional ball valve assemblies are available through EPI™ which allow the removal of the insertion style averaging tubes for service, calibration, cleaning, etc. The valve provides a means to seal off leaks of the process gas at the point of insertion after the probe assembly has been removed. Installation requires fitting the flow section to which the insertion probe assembly will be inserted with a threaded half coupling of the proper size to accommodate the ball valve retractor. In some instances, this requires direct threading together (or with a reducing bushing) of the retractor assembly. In other cases, it requires welding the half coupling in place and drilling a clearance hole through for the probe assembly. If the flow section is under pressure, a hot tap drill rig (not available through EPI) may be required.

The maximum pressure for insertion style flow meters is stated in the Manual for each product. To reduce the possibility of personal injury when servicing the flow meter, each size is rated such that the maximum force applied to the transmitter is approximately 25 pounds. Caution should be exercised if considering applying higher pressures, and AT HIGHER PRESSURES, A HOLDING DEVICE MAY BE REQUIRED TO PREVENT THE TRANSMITTER FROM BEING PROJECTED OUT OF THE PROCESS LINE WHEN REMOVING OR REPLACING THE TRANSMITTER ASSEMBLY.

Flow Meter Installation: Probe Insertion Depth Guidelines

EPI calibrates insertion flowmeters for positioning near the ISO Point-of-Average-Flow (0.243r). See the installation manual for calculation of the probe insertion depth (pipe OD to probe end) includes the point-of-average-flow, the x-factor, and the wall thickness of each nominal pipe size, as well as a further adjustment on smaller line sizes to be sure that the slot is fully inserted through the pipe wall. Any potential blockage effect created by inserting the probe assembly into the pipe to the depth listed has been accommodated by EPI™ as part of the calibration for the pipe size specified for the initial factory calibration. Therefore, the factory C-Factor value is now always “1”. Product-specific insertion depths are included in the Manual for that product.

Consult the factory for any additional C-Factor adjustments required if the flowmeter will be used in a pipe size other than that specified for the initial factory calibration.


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