Trane SCXG-SVX01B-EN manual Unit Control Components, RTM Module Board - Standard on all Units

general

Operation information

Unit Control Components

The Modular Series IntelliPakself- contained unit is controlled by a microelectronic control system that consists of a network of modules. These modules are referred to as unit control modules (UCM). In this manual, the acronym UCM refers to the entire control system network.

These modules perform specific unit functions using proportional/integral control algorithms. They are mounted in the unit control panel and are factory wired to their respective internal compo- nents. Each module receives and interprets information from other unit modules, sensors, remote panels, and customer binary contacts to satisfy the applicable request; i.e., economizing, mechanical cooling, heating, ventilation. Following is a detailed description of each module’s function.

RTM Module Board - Standard on all Units

The RTM responds to cooling, heating, and ventilation requests by energizing the proper unit components based on information received from other unit modules, sensors, remote panels, and customer supplied binary inputs. It initiates supply fan, exhaust fan, exhaust damper, inlet guide vane positioning or variable frequency drive output, and airside economizer operation based on that information.

Reference the RTM points list.

Note: Emergency stop and external auto/ stop, stop the unit immediately, emergency stop generates a manual reset diagnostic that must be reset at the unit human interface. External auto-stop will return the unit to the current operating mode when the input is closed, so this input is auto reset.

RTM Remote Economizer Minimum Position

The remote minimum position potentiometer, BAYSTAT023A, provides a variable resistance (0-270 ohms) to adjust the economizer minimum position from 0 to 100% when connected to the economizer remote minimum position

input of the RTM. The RTM must be selected as the source for economizer minimum position. If the RTM is the selected source for economizer minimum position, and if a valid resistance per Table O-GI-1 is provided to the RTM remote minimum position input, the OA cfm compensation function will not operate, even if enabled. “Default” is the only possible source for economizer minimum position when using the OA cfm compensation function.

Table O-GI-1. Economizer remote minimum position input resistance

input	economizer
resistance	min. position
0 - 30 ohms	0 %
30 - 240 ohms	0-100 % (linear)
240 - 350 ohms	100 %
> 350 ohms	N/A *

*Note: A resistance greater than 350 ohms is assumed to be an open circuit. The system will use the default minimum position value.

RTM Analog Outputs

The RTM has two 0-10 vdc outputs: one for the inlet guide vane option and one for the economizer option. These outputs provide a signal for one or two damper actuators. There are no terminal strip locations associated with these wires. They go directly from pins on the RTM circuit board to the actuator motor.

RTM Binary Outputs

The RTM has an output with pressure switch proving inputs for the supply fan. There is a 40 second delay from when the RTM starts the supply fan until the fan proving input must close. A fan failure diagnostic will occur after 40 seconds. This is a manual reset diagnostic, and all heating, cooling, and economizer functions will shut down. If this proving input is jumped, other nuisance diagnostics will occur. If the proving input fails to close in 40 seconds, the economizer cycles to the minimum position. This is a manual reset diagnostic. External control of the fan is not recommended.

VAV Drive Max Output

This is a single-pole, double-throw relay rated at a maximum voltage of 24 vac, two amps. The relay contacts of this relay switch when theunit goes from the occupied mode to the unoccupied mode bymeans of the occupied binary input. The contacts will stay switched during the

unoccupied and morning warmup mode. They will return to the position shown on the unit wiring diagram when the unit returns to the occupied mode. This binary output signals theVAV boxes or other terminal devices to go full open.

RTM Alarm Relay

This is a single pole, double throw relay rated at a maximum voltage of 24 vac, two amps max. Relay contacts can be programmed from the unit human interface. This relay can be programmed to pick up on any one or group of diagnostics from the unit human interface.

Status/Annunciator Output

The status annunciator output is an internal function within the RTM module on CV andVAV units. It provides:

a. diagnostic and mode status signals to the remote panel (LEDs) and to the Human Interface.

b. control of the binary alarm output on the RTM.

c. control of the binary outputs on the GBAS module to inform the customer of the operational status and/or diagnostic conditions.

Occupied/Unoccupied Inputs There are four ways to switch to occupied/unoccupied:

1.Field-supplied contact closure hardwired binary input to the RTM

2.Programmable night setback zone sensor

3.Tracer Summit

4.Factory-mounted time clock

VAV Changeover Contacts

These contacts are connected to the RTM when daytime heating onVAV units with internal or external hydronic heat is required. Daytime (occupied) heating switches the system to a CV unit operation. Refer to the unit wiring diagram for the field connection terminals in the unit control panel. The switch must be rated at 12 ma @ 24 VDC minimum.

External Auto/Stop Switch

A field-supplied switch may be used to shut down unit operation. This switch is a binary input wired to the RTM. When opened, the unit shuts down immediately and can be cancelled by closing the switch. Refer to the unit wiring diagrams (attached to the unit control panel) for proper connection terminals. The switch

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