Point Information

Physical Point

A physical point is a piece of field equipment plus its physical connection to a unique termination in the field panel. An example of a physical point would be a fan motor starter wired to a single termination in a field panel. A physical point is either an input point or output point. A physical point is further classified as analog or digital.

• An input point collects information from the environment and provides the information, or input, to the field panel. Input points indicate facility conditions such as temperature, and the state of equipment, such as whether a fan is on or off.
• An output point acts upon the building equipment and is controlled by signals, or output, from the field panel. You use output points to command equipment such as fans and pumps.
• An analog point uses a range of values to represent a condition which has more than two states, for example temperature and air velocity.
• A digital point uses two states, such as on/off and open/closed, to represent the status of equipment such as fans and pumps.
• A digital point is either:
• latched and changes states via a switch (sustained contact with a physical device), such as when you turn a light on or off.
• pulsed and changes states by sending a series of electrical pulses (momentary changes in voltage), such as when you press a push-button on a fan motor starter.

 

Virtual Point

A virtual point is a "dummy" output point (analog or digital) that resides in a field panel but does not have a physical connection to a piece of equipment.

Virtual points store operational values and are used as setpoints, trigger points, and mode points. The value of a virtual point can be set by a control program instruction or by an operator. Virtual points are primarily used in Powers Process Control Language (PPCL).

Using a virtual point for a set point

A set point is a virtual point that stores a desired point value such as a temperature setting. Points that monitor inputs, such as temperature, report actual values. For the system to make adjustments to control equipment, the system must compare an actual point value to a desired value (set point).

Set points provide an easy method for you to adjust a building condition. When you want to change a building condition, you control a set point rather than having to command several physical points. For example, if you want to lower the temperature in a room, you lower the temperature set point, rather than sending separate commands to physical points for fans, chillers, and dampers.

Using a virtual point for operational values

Virtual points are often used to store operational data and results from calculations. For example, a virtual point can be the average temperature value for six different buildings. Virtual points can also store the coldest and warmest temperature readings from an outside air sensor.

Applications such as PPCL, use virtual points to store different types of values. For example, PPCL uses virtual points to store times and date information that is necessary to accomplish building control.

Logical Point

A logical point is an entry in the workstation software and field panel databases that represents a piece of equipment or a building condition you want the software to monitor or control. Each logical point can have one or more physical and/or virtual points associated with it. The point grouping is referred to collectively by a single, unique logical point name. You reference the logical point when you use the software to command, monitor, and store information for points. For more information on logical points, see Logical Point Types.

 

Logical Point Type List

When you add a point with the Point Editor, you must specify the point type and other information which describes the characteristics of the point, such as the point name, description, address, and alarm characteristics. The point type indicates whether the point is an input or output, whether the point is analog or digital, and the number of physical points used. The information that the software requires you to supply for a point depends on the point type. The point types are:

• LAI - Logical Analog Input. A logical point type that indicates the value of one analog input point. For example, sensors that measure analog values such as flow rate, temperature, pressure, and humidity.
• LAO - Logical Analog Output. A logical point type that commands one analog output point. For example, damper positioners, valve positioners, and motor speed control.
• LDI – Logical Digital Input. A logical point type that indicates the status of one latched digital input point for a two-state (On/Off) device. For example, door contacts, smoke and low temperature detectors, damper end switches, differential pressure switches, and flow and fan proof switches.
• LDO – Logical Digital Output. A logical point type that commands one latched digital output point for a two-state (On/Off) device. For example, lighting, chiller, and boiler switches, fan and pump motor starters, and 2-position valves and dampers.
• L2SP - Logical Two State Pulsed. A logical point type that commands two pulsed digital output points (On and Off) and indicates the status of one optional latched digital input point (proof). For example, two-state (On/Off) push-button motors that provide proof, such as fan motors.
• L2SL – Logical Two State Latched. A logical point type that commands one latched digital output point and indicates the status of one latched digital input point (proof). For example, two-state (On/Off) motors that provide proof, such as fan motors.
• LFSSL - Logical Fast/Slow/Stop Latched. A logical point type that commands two latched digital output points (Fast/Stop and Slow/Stop) and indicates the status of one optional latched digital input point (proof). For example, three state (Fast/Slow/Stop) motors that provide proof, such as two-speed fan motors.
• LFSSP - Logical Fast/Slow/Stop Pulsed. A logical point type that commands three pulsed digital output points (Fast, Slow, and Stop) and indicates the status of one optional latched digital input point (proof). For example, three state (Fast/Slow/Stop) push-button motors that provide proof, such as two-speed fan motors.
• LOOAL – Logical On/Off/Auto Latched. A logical point type that commands two latched digital output points (On/Off and Auto) and indicates the status of one optional latched digital input point (proof). For example, three state (On/Off/Auto) motors that provide proof, such as fan motors.
• LOOAP - Logical On/Off/Auto Pulsed. A logical point type that commands two pulsed digital output points (On and Off) and one latched digital output point (Auto). This point can also indicate the status of one optional latched digital input point (proof). For example, three state (On/Off/Auto) push-button motors that provide proof, such as fan and pump motors.
• LPACI - Logical Pulse Accumulator Input. A logical point type that counts the number of pulses (momentary contacts) for one digital input point. For example, a LPACI point can track electrical consumption by totaling the number of contact closures from a KWH power meter or a flow meter.
• LENUM – Logical Enumerated. A logical point type that commands points that have multiple values or states and each value or state has text assigned to it. A LENUM point can be a physical or a virtual point that stores operational values for applications such as SSTO.
  In a fire system, LENUM points are used to record values for smoke detectors and other devices that have multiple active states (inactive, maintenance, dirty, pre-alarm, alarm verify, active, etc.)
  For automatically-generated LENUM’s associated with Event Enrollment Objects, the LENUMs are used locally at the workstation and never downloaded to a panel. You cannot delete these types of LENUMs.

 

Basic Point Types

There are four basic types of points:

• Analog Input (AI) Point - A point that receives a signal that represents a condition which has more than two states. For example, flow rate sensors (water or air), temperature sensors (room or duct), pressure sensors (static or velocity), and humidity sensors (room, duct or outdoor).
• Analog Output (AO) Point - A point that sends a signal to command equipment which has more than two states. For example, damper or valve positioners, fan inlet vane controllers, motor controllers, or electric heater controllers.
• Digital Input (DI) Point – A point that receives a two-state signal such as a On/off and Open/Closed. For example, low temperature detectors, differential pressure switches, flow proof switches, smoke alarm switches, filter switches, and door closures.
• Digital Output (DO) Point - A point that sends a two-state signal such as On/Off and Open/Closed. For example, 2-speed fan motor starters, 2-position valves and dampers, pump motor starters, lighting switches, and chiller and boiler switches.

Point Addressing

Each point has a unique address which identifies where the equipment point terminates in the field panel and the network on which the point information is transferred. The address format for a point depends on the revision of firmware in the field panel that contains the point. The workstation software can detect the revision of firmware that is in the field panel and displays the appropriate address format in the Point Address field.