Bronkhorst Mass Flow - Manual (Page 20)

BRONKHORST HIGH-TECH B.V.
3 Operation
3.1 General
The Bronkhorst High-Tech instruments are designed in such a way that they will meet user process
requirements in the best possible way.
Flow / pressure meters and controllers are powered from a dc power source. When providing your own
power supply be sure that voltage and current rating are according to the specifications of the instrument(s)
and furthermore that the source is capable of delivering enough energy to the instrument(s).
Cable wire diameters should be sufficient to carry the supply current and voltage losses must be kept as low
as possible. When in doubt: consult factory.
3.2 Power and warm-up
Before switching on power check if all connections have been made according to the hook-up diagram,
which belongs to the instrument.
It is recommended to turn on power before applying pressure on the instrument and to switch off power after
removing pressure.
Check fluid connections and make sure there is no leakage. If needed purge the system with a proper fluid.
For a gas instrument only purging with gases is allowed. Liquid instruments may be purged with either a gas
or a liquid, whatever is needed for the purpose.
Turn on power and allow at least 30 minutes to warm up and stabilize. In cases where no electronics are
involved (valves only) warming up is not needed.
During warm-up period, fluid pressure may either be on or off.
3.3 Zeroing
In general the zero point of each instrument is factory adjusted. If so required the zero point of the instrument
may be re-adjusted.
Zero points must be adjusted to read approx. 0.2%. The circuit will cut off signals below zero to prevent
negative zero drift. When adjustment is required, first make sure that there is a positive deviation, and then
slowly adjust the readout to read approx. 0.2%. To be sure that there is no accidental flow or pressure level
other than zero, adjustment is done best when the instrument is not part of a system.
3.4 Start-up
Turn on fluid supply gently. Avoid pressure shocks, and bring the instrument gradually up to the level of the
actual operating conditions. Also switch off fluid supply gently. In case of liquid control be sure to remove all
trapped gas bubbles from the system. The purge connection on top of the control valve can be used for this
purpose.
3.5 Operating conditions
Each instrument has been calibrated and adjusted for customer process conditions.
Controllers or valves may not operate correctly, if process conditions vary too much, because of the
restriction of the orifice in the valve.
For flowmeters performance and accuracy may be affected tremendously if physical fluid properties such as
heat capacity and viscosity change due to changing process conditions.
page 20 9.17.001