CONTROL SYSTEM

BURNER CONTROL SYSTEM

Figure 47.  R7910A1138 CONTROL SYSTEM

The R7910A1138 is a burner control system that provide heat control, flame supervision, circulation pump control, fan control, boiler control sequencing, and electric ignition function. It will also provide boiler status and error reporting. Multiple boilers can be joined together to heat a system instead of a single, larger burner or boiler. Using boilers in parallel is more efficient, costs less, reduces emissions, improves load control, and is more flexible than the traditional large boiler. Control System consists of:

R7910A1138 Control Device.

S7999B Touchscreen Display—required for setup and ModBus communication but not required for the system to operate once the R7910A1138 is programmed.

S7910A Local Keyboard Display Module.

Flame Rod .

Temperature Sensor, NTC Type 10KΩ at 77°F (25°C) or 12KΩ at 77°F (25°C).

Limit Sensor, NTC Type 10KΩ at 77°F (25°C).

24V Digital I/O.

OVERVIEW

Functions provided by the R7910A1138 include automatic boiler sequencing, flame supervision, system status indication, firing rate control, load control, CH/DHW control, limit control, system or self-diagnostics and troubleshooting.

The R7910 maximum version of the controller offers:

1.NTC-temperature sensor for:

Outlet Limit And Temperature.

Stack Temperature Limit and Temperature.

Inlet Temperature.

Outdoor Temperature (R7910 only).

2.Modulating output PWM-driven rotation speed controlled DC-fan for optimal modulation control.

3.Three Pump Outputs with 5 selectable operation modes.

4.24VAC:

Output control of gas valve (Pilot and Main) and External Ignition Transformer.

Digital inputs for room limit control, high limit control, Gas pressure switch, low water cutoff.

5.External spark transformer.

6.Flame Sensor.

7.Test jacks for flame signal measurement from either a flame rod or UV flame sensor.

8.Alarm Output.

Figure 48.  GENERAL R7910A1138 BOILER SCHEMATIC

The above figure shows two loops of heat control: Central Heating (CH), and an optional second loop for Domestic Hot Water (DHW) can be configured on each R7910A. The DHW loop transfers heat from the boiler outlet to hot water appliances in conjunction with the primary system heat loop. Priority assignment to each heat loop can be configured to specify which loop gets serviced first.

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A.O. Smith 2600, 3400, 1700, 2000 instruction manual Burner Control System, Overview

3400, 1700, 2000, 2600 specifications

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