Emerson ControlWave EFM Instruction Manual page 20

ControlWave EFM Instruction Manual
1.9.11 Sampler and Odorizer
1.9.12 Flow Rate Control – DCC (Jog Control) Using PID
1.9.13 Pulse Output for External Totalizer or Sampler
1.9.14 Nominations
1-16
Samplers are external devices which measure the quality of the gas
stream. Because natural gas is odorless and colorless, devices called
odorizers inject an additive to the gas stream that allows people to
detect the presence of natural gas in the event of a gas leak.
To configure the EFM to perform flow rate control you wire the two
discrete outputs to the open and close inputs of a controller. The EFM
uses a proportional/integral/derivative (PID) algorithm to cause the
measured rate of flow to match a user-entered setpoint. When the flow
rate falls below the setpoint, the open output is pulsed. When the flow
rate rises above the setpoint, the close output is pulsed. The PID
equation calculates the duration of the open or close pulse; the
minimum pulse duration is 1.0 seconds. The user changeable parameters
are:
 Flow setpoint in MSCFH
 Deadband in % of setpoint
 Proportion gain
 Integral time in repeats/minute
 Derivative time in seconds
 Valve travel time (full close to full open)
 Process control limiting
 Pressure override limits
The flow control algorithm runs once per second.
When you configure the EFM to provide a pulse output based on
volume, the operator provides a control volume and pulse duration.
After each calculation cycle, the application compares an internal
volume accumulator to the control volume. If the accumulator exceeds
the control volume then a pulse is output and the accumulator is reduced
by the volume represented by the pulse. You can use the pulse output to
drive an external totalizer, odorizer, gas sampler, or similar device.
Nominations allow you to configure the EFM to allocate precise
amounts of gas flow (called nomination values) during specific time
periods, called nomination periods. When the nomination value is
reached, the system performs an action (such as opening or closing a
valve). Prior to reaching the nomination value, the application compares
the volume/energy to a configured alarm level and generates an alarm
when the volume/energy meets or exceeds that alarm level.
Introduction Revised Dec-2013