Onicon F-5100 Insertion Manual do Utilizador descarregar pdf (Página 30)

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F-5100 Insertion Thermal Mass Flow Meter Manual 05/15 - 0663-20 / 18333 Page A-3

ZERO FLOW CALIBRATION TEST

The zero ow calibration test provides a simple, yet effective, method for periodic eld validation of

the factory calibration. Prior to shipment to the customer, each ONICON F-5000 series ow sensor

undergoes a multipoint calibration. In this process, signal levels are recorded at a series of known

velocities over the specied operating range. The last data point taken in this process is taken at zero

ow (zero velocity). The value recorded at zero ow is part of the calibration record provided with the

sensor and is stamped on the sensor nameplate. By utilizing the mW output displayed by the sensor, it

is possible to duplicate the factory no ow condition (zero velocity) test in the eld.

Successfully duplicating this test provides eld validation of the current calibration. A successful

zero ow test conrms that the ow sensor circuitry operating characteristics have not changed and

validates that the zero velocity data point has not shifted or drifted. It also veries that the sensor

assembly is clean and undamaged and does not require visual inspection. It essentially provides a

means to validate that the sensor is operating properly and can be used as part of a quality assurance/

preventative maintenance program or in lieu of scheduled annual factory calibrations.

IMPORTANT NOTE

The original factory zero ow calibration was performed with a vertically oriented sensor installed

through a valve located on the top of a horizontal test pipe. If the sensor is installed in a different

orientation the output at zero ow will be slightly different.

Depending on the orientation, sensors inserted horizontally into a pipe may increase the reading

by as much as 5-6 mW.

There are 3 ways to validate the sensor’s zero ow calibration.

WARNING

SYSTEM MAY BE UNDER HIGH PRESSURE. When removing the ow sensor, be sure to grasp

the electronics enclosure rmly by hand before slowly loosening the compression tting. Failure

to do this will allow the pressure in the pipe to suddenly and rapidly force the sensor from the

pipe causing serious injury. The hand effort required to hold the sensor will be 0.2 times the pipe

pressure.

WARNING

Do not attempt to remove the sensor from a pipe pressurized to greater than 250 PSIG. For pipes

pressurized above 250 PSIG isolate ow and relieve pressure in the pipe before attempting to

remove the sensor.

Method 1

1. Close valves in the process supply line to stop all ow in the pipe where the sensor is located.

2. Wait up to 2 – 3 minutes to allow the sensor reading to stabilize at zero and note the mW

reading on the display.

3. Compare the reading to that stamped on the nameplate. The two readings should agree within ± 5mW.

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Onicon F-5100 Insertion Manual do Utilizador Página 30