Chapter 3 Operation
Series 810 Instruction Manual
A 5.1 VDC reference is provided for internal and external setpoint
command pots. The reference provides approximately 0.125 volts
headroom to allow for external cabling and ensures that the instrument will
always reach full scale when using these inputs.
DIP switch 6 has no function at this time.
Over-Range
If the flow rate exceeds the full-scale range listed on your Mass-Trak's data
label, the output signal and digital display will read a value above full-
scale. The Mass-Trak has not been calibrated for over-ranged flows and
will be both non-linear and inaccurate if an over-range condition exists.
The 0-5 VDC (0-10 optional) and 4-20 mA outputs can exceed full scale by
as much as 50%, or more. On the digital display, the display cannot
exceed the four digits 1999. If the flow rate exceeds 1999, the right-most
digits will appear blank and only the left-hand "1" will appear on the
display.
Once the over-range condition has been removed, it may take several
minutes for the Mass-Trak to recover and resume normal operation. An
over-range condition will not harm the instrument.
Cold Sensor Lockout Circuit
Mass-Trak controllers incorporate a safety circuit that closes the valve
when
a fault condition is detected that could result in uncontrolled flow
(valve
wide open). The circuit operates by monitoring the temperature of
the
sensor elements and forcing the output high if the temperature falls below
a
preset limit. There are several conditions under which this may occur:
1.
Operation at a temperature below that for which the instrument is rated.
2.
Power failure while running at or near full-scale. Upon resumption of
power, the valve will remain closed until the minimum operating
temperature is reached.
3. A rapid, uncontrolled increase of gas flow through the transducer can
create a cooling effect on the sensor, driving it below the preset limit.
One possible scenario where this may occur is if backpressure
downstream from the instrument is suddenly reduced. Another scenario
is if the gas pressure should suddenly go to zero while the set point
remains at a fixed position. This could occur if a valve upstream is
closed, for example. When the pressure is re-instated, a rapid,
uncontrolled gas flow could occur activating the cold sensor lockout
circuit.
3-4
IM-81
