Table of Contents
Advertisement
301/303/305/306/307 Flowmeters and Controllers Instruction Manual
Controlling Other Process Variables (External Input)
Flow controllers usually control mass flow. The control loop
opens and closes the valve to make the output flow signal
match the command signal.
removed from a system to control some other process variable.
This could be system pressure, oxygen concentration, vacuum
level etc. If this process variable has a sensor that can supply
an analog signal proportional to its value, the flow controller
may be able to control this variable directly.
output signal could be 0-5 volts, 0-10 volts (or 4-20 mA for units
with 4-20 mA boards) or any value in between.
On the controller card, JP4 sets whether the control loop
controls mass flow (5,6) or an external process variable (7,8).
See right. This process variable signal must be supplied on pin
13 of the D connector for H pinout units (pin 12 for U pinouts)
of the meter card. When the controller is set for external
input, it will open or close the valve as necessary to make the
external process variable signal match the command signal. If
the process variable has a response time that is much faster or
slower than the flow meter signal it may be necessary to adjust
the gain potentiometer (see section 2.11).
Command Input
The flow controller will operate normally with any command input signal between 0-5 volts (4-20 ma for
units with 4-20 ma input/output cards) If the command signal exceeds ±14 volts it may damage the
circuit cards. During normal operation the control loop will open or close the valve to bring the output
of the flow meter signal to within ± 0.001 volts of the command signal. The flow signal will not match
the command signal if there is insufficient gas pressure to generate the desired flow. If the command
signal exceeds 5 volts, the controller will continue to increase the flow until the output matches the
command signal. However, the flow output does not have any guaranteed accuracy values under these
conditions.
If the command signal is less than 2% of full scale (0.1 volts or 4.32 ma) the valve override control circuit
will activate in the closed position. This will force the valve completely closed regardless of the flow
signal.
Valve Override Control
The valve override control line provides a method to override the loop controller and open or close the
valve regardless of the flow or command signals. During normal operation this line must be allowed to
float freely. This will allow the loop control to open and close the valve as it requires. If the valve
override line is forced high (> +5 volts) the valve will be forced full open. If the valve-override line is
forced negative (< -5 volts) the valve will be forced closed.
EAR99 Technology Subject to Restrictions Contained on the Cover Page
Occasionally, gas is added or
This analog
Page 20 of 32
Advertisement
Table of Contents
