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Zero CAL-CHECK™ Calibration Validation Feature

Zero CAL-CHECK™ is a companion test to the CAL-V™ Calibration Validation feature available on the Fox Model FT3 Thermal Mass Flow Meter & Temperature Transmitter.  Where CAL-V™ tests the functionality of the sensor and its associated signal processing circuitry, Zero CAL-CHECK™ does the following:

  • Checks for build-up on sensor that could affect calibration
  • Further validates the zero stability of the meter
  • Checks thermal conductivity (heat transfer) repeatability of the sensor

Unlike CAL-V™, which may be performed in the pipe and at process conditions, Zero CAL-CHECK™ must be performed at zero flow to ensure a valid test result.  Depending on the test selected – insitu or out of pipe – zero flow will either be compared to a customer-established field baseline or factory baseline as illustrated in the image below.


As the illustration above suggests, there are multiple ways of achieving zero flow conditions in order to conduct the Zero CAL-CHECK™ test.

Insitu Zero CAL-CHECK™ Configurations


Insitu Zero CAL-CHECK™ testing can be achieved in one of two common ways:


The first insitu option is achieved through the use of a packing gland assembly that may be ordered as an option for most inline- or insertion-type meters.  The assembly allows the operator to retract and isolate the sensor from the process in order to conduct the Zero CAL-CHECK™ test.  This is particularly beneficial for applications in which the process is not easily stopped.


The second insitu option, if space allows, is to redirect the flow through a bypass pipe section in order to isolate the sensor of the meter in the position where it has been installed.  While the flow is redirected, the Zero CAL-CHECK™ test can be performed.  Once the test is complete, the valves to the bypass may be closed and flow may be directed back to the meter’s sensor where flow monitoring can continue as normal.


Out of Pipe Zero CAL-CHECK™ Configurations


If space limitations prevent insitu testing at zero flow as listed to the left, then out of pipe testing must be performed.


With this configuration, the meter must be removed from the process, the test performed, and then the meter returned to the process after testing has been completed.


Due to the high sensitivity of the PowerPro™ sensor, it is necessary to isolate the sensor once the meter has been removed from the pipe.  Therefore, Fox provides a sensor cover when the meter is shipped to the customer.  An alternative to the sensor cover is to use a bottle or other closed container in order to isolate the sensor and achieve the “no flow” condition necessary to perform the Zero CAL-CHECK™ test.


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Full Calibration Validation with CAL-V™ and Zero CAL-CHECK™ Tests


A passing CAL-V™ in-situ sensor and electronics test coupled with a passing Zero CAL-CHECK™ test provides complete validation of flow meter calibration accuracy including confirmation that the sensing elements are clean.  It is recommended CAL-V™ and Zero CAL-CHECK™ be performed annually or as required by federal, state and local agencies, if applicable.

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Fox Thermal Instruments, Inc. 399 Reservation Road | Marina, CA 93933 | Phone: (831) 384-4300 | Fax: (831) 384-4312 | Copyright 2005-2014