Slant/Fin CHS-399 - Manual (Page 13)

CHS Series Controller and Display
│
Slant Fin Corp.
11
Use of 4-20mA Input
Setpoint source – If “Local” is selected as the “Setpoint source”, the “CH setpoint” value entered on the screen,
depicted in Figure 2-10, 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 “CH 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.
Mod rate source – The Slant/Fin CHS controller supports two methods of burner modulation for CH, selected
by the “Mod rate source” parameter, depicted on Figure 2-10; the factory set method is by internal PID
algorithm. The installer has the option to use a 4-20mA signal from an external control to directly modulate the
burner. Rates vary (see Section 2.4.5 Modulation Config) from minimum at 4mA to CH maximum at 20mA.
The 4-20mA signal does not create burner demand; a call for heat must be present; i.e. CHI input made when
“Demand Switch” = LCI..
Table 2-6 Central Heat Configuration Parameters
Parameter Description Factory Settings
Demand
switch *
Source of CH demand:

Sensor only (modulation sensor – no contact closure required)

LCI (contact closure of “CH1” to “R”, i.e. via a thermostat)
LCI
Setpoint
source *
Select the Central Heat setpoint source:

Local (control references “CH setpoint” setting)

4-20mA with sensor on/off [remote source]
Local
CH setpoint
Setpoint value for CH modulation. If “Outdoor reset” is set to “Disable”, this is the
target temperature at the “Modulation sensor”. If “Outdoor reset” is set to “Enable”,
this is the maximum target temperature at the “Modulation sensor” (see Section
2.4.1.2 Outdoor Reset Config). Range 60°F to 190°F
180°F
Off hysteresis
Value added to CH setpoint to determine water temperature at which the burner will
shut off e.g. if CH setpoint is 180°F, and CH off hysteresis is 10°F, the burner will be
shut off at 190°F. Range 2°F to 20°F
10°F
On hysteresis
Value subtracted from “CH setpoint” to determine water temperature at which the
burner will fire e.g. if “CH setpoint” is 180°F, and “CH on hysteresis” is 20°F, the
burner will fire at 160°F. Range 2 °F to 40°F
20°F
Modulation
sensor *
Select which sensor Central Heat will modulate to:

Outlet

Inlet

S10 [System (pipe) temperature sensor]
Outlet sensor
Mod rate
source *
Select which source controls the modulation rate:

Local [PID control]

4-20mA with sensor on/off [remote source]
Local
* = Password protected