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Series 820 Instruction Manual Chapter 4 Maintenance & Repair
IM-82-C 4-9
Transducer Calibration
Calibration of Sierra’s flow meters requires a calibration standard of
at least four times the accuracy of the transducer. Sierra’s Cal-Bench
Automated Primary Calibration System is the preferred method of
calibration and is used at the factory for all calibrations from 10 sccm
up to 50 slpm. Most calibrations can be performed with a digital
voltmeter (DVM) or multimeter with 0.25% accuracy and four digits,
dry nitrogen and the K-factor tables included in this manual. Flow
meters require a metering valve for setting a constant flow rate.
The following procedures are offered as guidelines for calibration.
It is always best to return the transducer to the factory for calibra-
tion. Calibration checks and minor adjustments to the zero and full
scale are made via the access ports in the enclosure. If the linearity
needs adjustment (when installing a different bypass to change the
range) skip Step 2 and Step 3. If linearity does not need adjustment,
complete only Steps 1 through 3.
Step 1. Warm Up
Plug in the unit to be calibrated and allow at least 30 minutes warm
up time before attempting any adjustments.
Step 2. Zero Adjust
Slide open the zero and span access doors. Connect a DVM or mul-
timeter to the transducer output pins. Adjust the zero potentiometer
for 0.0 volts (4 mA) at zero flow.
Step 3. Check Full Scale
Generate full scale flow using a metering valve in-line with the unit
under test. Compare the indicated flow rate with the flow standard
reading. If they agree to within ±10%, adjust the span potentiometer
for exact agreement. If the readings do not agree within ±10%, at-
tempt to determine the cause of disagreement. Possibilities are:
• leaks in the system or in the transducer
• wrong or improper use of K-factor
• wrong or improper correction for temperature and pressure
• partially clogged or dirty sensor tube
• replacement of components in the flow path do not exactly match
the original parts
This completes transducer calibration. To adjust linearity, continue
with Step 4.
Caution!
It is important that this
transducer be calibrated
only by qualified personnel.