CleaverBrooks CFC-500 Operation, Service And Parts Manual page 100

Section 4 — CFC Commissioning
Depending on the quality of the remote input signal, the modulation
rate or operating set point may fluctuate slightly because of small
changes in the measured current signal or because of induced
noise. Under the Modulation configuration group, the "4-20mA
input Hysteresis" setting may need to be adjusted to avoid
undesired fluctuations in the either the modulation rate or operating
set point. The default setting is 0.2mA and can be increased to
essentially filter out small fluctuations of the input signal. It may
take some trial and error to establish the optimum input hysteresis
setting for a particular system.
If at any time the remote 4-20mA input signal is disconnected, the
Falcon control will indicate "OPEN" or "LOCAL" under the 4-20mA
input value at the operation screen. The boiler will then operate on
its local set point and PID modulation control. Once the 4-20mA
signal is reestablished, the boiler will resume operation under
remote control.
Rate Limiting/Override
For safety reasons or to accommodate special operating conditions,
the CB Falcon incorporates a number of control functions that either
limit the modulation range or set the firing rate to a specific value.
These functions include Delta T limiting, Slow Start, and Forced
Rate. See Appendix A for a complete listing of control functions with
detailed descriptions and parametrization instructions.
Delta T limiting is designed to reduce the firing rate in case of an
excessive difference between the inlet and outlet temperatures.
Sensor connections to the CB Falcon are at J8-4 and -5 (inlet
temperature) and J8-8,-9, and -10 (outlet temperature). Delta T
limiting includes an Inversion Detection mode which when enabled
becomes active in case the inlet temperature is higher than the
outlet temperature (indicating reverse water flow through the
boiler).
Forced Rate limiting causes the burner to stay at a fixed firing rate
for a fixed time period immediately after lightoff, following the Run
Stabilization period (if any). The forced rate period is optionally
followed by a Slow Start function that limits the ramp-up speed of
the firing rate whenever the water is colder than a user-specifiable
threshold. Slow Start can help reduce set point overshoot, high limit
trips, and frequent cycling.
Configurable Pump/Aux Relay Contacts
The CB Falcon Pump/Aux Relay outputs are configurable by means
of six identical Pump Control Blocks. Each control block has seven
parameters:
Pump Options (2 parameter blocks) - determine pump on/off
conditions
Start Delay - if burner is just starting up, timer will delay pump
turning on
4-30 Part No. 750-263