Use Of 4-20Ma Input - Slant/Fin CHS-85 Instructions Manual

CHS Series
Table 2-10 Lead Lag Master Configuration Parameters
Parameter Description
Master Enable or Disable Lead Lag Master. One (and only one) unit must be set to
"Enable" for Lead Lag operation to function.
enable *
Select the Lead Lag setpoint source:

Local (control references "Setpoint" setting)
Setpoint

4-20mA (control references 4-20mA signal from an external control). "Outdoor
source *
reset enable" must be set to "Disable" when using a 4-20mA signal; see Section
2.4.3.3 Lead Lag Outdoor Reset.
Setpoint Setpoint value for Lead Lag modulation. Range 60°F to 190°F.
Value added to the "Setpoint" to determine water temperature at which the burner
Off
will shut off. Example: If "Setpoint" is 150°F, and "Off hysteresis" is 15°F, the
Hysteresis *
burner will be shut off at 165°F. Range 5 °F to 70°F.
Value subtracted from "Setpoint" to determine water temperature at which the
On
burner will fire. Example: If "Setpoint" is 150°F, and "On hysteresis" is 10°F,
Hysteresis *
burner ignition occurs at 140°F. Range 2°F to 40°F.
Gain applied to the proportional term of the LL PID control algorithm. Range 5 to
P Gain *
50 (no units). Decrease to slow rate of control response.
Gain applied to the integral term of the LL PID control algorithm. Range 5 to 50 (no
I Gain *
units). Decrease to slow rate of control response.
Base load Maximum modulation rate of all firing units when other units are still available and
common * idle. Range 25 - 100%.
* Password protected

Use of 4-20mA Input

Setpoint source – If "Local" is selected as the "Setpoint source", the "Setpoint" value entered on the screen,
depicted in Figure 2-16, is used for control. If 4-20mA is selected as the "Setpoint source", the boiler
determines its setpoint from the 4-20mA signal. The setpoint is calculated from a factory-set scale between 60°F
corresponding to 4mA, and 190°F corresponding to 20mA. If the 4-20mA input signal is invalid, out of range, or
absent, the "Setpoint" is used until the signal is valid again. Regardless of the "Setpoint source", "Local" or "4-
20mA", the controller's internal PID algorithm modulates the burner. The 4-20mA signal does not create
burner demand; a call for heat must be present at the CH2 (LL) input.
Controller and Display
│
Slant Fin Corp.
Factory Settings
Disable
Local
150°F
15°F
10°F
30
15
70%
17