### BACnet Bypass Control The information below provides a FULL description of this microblock and all of its properties. What information you see and what you can do with it depends on your license and the application you are in, and in some cases, a controller's driver version. This microblock is compatible only with Carrier controllers.
Microblock family | I/O Point microblocks
Icon and symbol |
What it does | Controls the bypass damper based on the commanded position input wire. Converts the pressure sensor count to pressure and output this value to the DUCT SP wire. Allows for the configuration of the duct static pressure setpoint and the maximum static pressure setpoint during LAT override. Enables testing and balancing through the WebCTRL® interface. Calibrates the airflow sensor readings at design setpoint and zero calibration of sensor when AHU fan is off. Calibrates full open and closed damper positions. Applies to the following controllers: VVT Bypass
Click for details below How it works Inputs and outputs Properties Static Pressure Input Properties Alarms Simulation Tips and tricks BACnet object property addresses
#### How it works The microblock adds the airflow sensor output with any required zero offset and slope adjustment and converts it to a useable static pressure reading. This value is place on the DUCT SP output wire to be used by the control program for static pressure control. The bypass damper is controlled by the COMMANDED POS input and the internal damper position feedback signal, no error control is used at this level. The output is calculated using integral control and is active until the damper position equals the COMMANDED POS. The Bypass microblock provides the control program with the working static pressure setpoint, this is normally the configured base static pressure setpoint. When LAT override is in effect, the microblock calculates the working static pressure setpoint based on a linear value between the configured base setpoint and the configured maximum LAT setpoint. This allows for increased static pressure when the LAT (Leaving Air Temperature) of the AHU exceeds a configurable limit. Test and Balance The microblock allows for direct calibration of the sensor at the configured duct static setpoint. When the Static Pressure Setpoint button is selected, the microblock checks for LAT override, if active, no sensor calibration will be performed. With no LAT override (LAT OVRRIDE=0%), the CAL ACTIVE output goes true (yes) and the control program controls to the configured duct static pressure setpoint. THE DAMPER MOVE input wire will equal 0 when the setpoint is reached and the damper has stopped moving. The bypass controller is now at the configured setpoint and actual pressure readings obtained from the air balancer may be entered. The current sensor reading is calibrated to this new value and the offset value is retained for future pressure sensor count conversions. When the Auto Zero button is selected, the microblock ensures the air source fan is off, reads the current raw count and determines a zero offset to be used in future sensor count conversions. If AHU MODE equals any number other than “1”, no zero calibration takes place. The Damper Full Open and Damper Full Close buttons force the damper to the fully opened or closed position. The damper position feedback values for these positions are stored and used by the damper control routine. Normal control is suspended until the Automatic Control button is activated, or until one hour of inactivity has passed, at which time the Test and Balance mode will automatically be terminated.
#### Inputs and outputs Inputs
COMMANDED POS | The current desired position (%) of the bypass damper.
LAT OVRRIDE | The current calculated value (%) between the configured (base) static pressure setpoint and the maximum configured LAT override setpoint required to satisfy LAT limits.
AHU MODE | A Multi-state variable that indicates the current mode of the associated Air Handling Unit. The AHU Modes are as follows: Off Warmup Heat Cool Freecool Pressure Evac Vent
DAMPER MOVE | A binary value that indicates whether the damper has achieved the commanded position (0), or if it is still moving (1).
Outputs
DUCT SP | The current duct static pressure (in H2O).
WSP SETPNT | Working Static Pressure setpoint (in H2O). This is the static pressure setpoint that the bypass is controlling to, and includes any LAT override that might be in effect.
DAMPER POS | Current position of the bypass damper (% open to bypass).
SP SETPNT | The configured (base) duct static pressure setpoint.
MAX LAT SP | The configured maximum LAT duct static pressure setpoint. This is the maximum duct static pressure that will be used during LAT override.
CAL ACTIVE | A binary value that indicates if the airflow sensor static pressure reading is being calibrated (yes/no) in the Test & Balance screen. NOTE LAT OVERRIDE must be 0% before the Cal Active output goes to “yes”.
#### Properties TIPS Alt+click any value in the WebCTRL® or Field Assistant interface to view property details, including its editing privilege and expression (location path) for use on graphics. You can right-click some properties in the EIKON® Property Editor and select Make editable or Make read-only to determine that property's functionality in your system.
Display Name | The microblock label used in the interface. You can use any characters (including spaces) in this field, except for the " character.
Reference Name RefName | Use the default reference name unless you want a more descriptive name for graphics or network links. Limitations: lower case only limited to 40 characters cannot begin with a number must be unique within a control program
Description | (optional) A BACnet-visible microblock description.
Editing Privilege | Preset - Each microblock property has an appropriate privilege or role assigned to it. You can use Global Modify in the WebCTRL® interface to find out what the actual privilege is. CAUTION If you change the Editing Privilege from Preset, the privilege you select will be used for all properties of this microblock, which is not always desirable.
Units | The BACnet engineering unit of measurement of the microblock's present value.
Hardware Configuration
Direction: CW = | Close - Turn the damper motor clockwise to close the damper. Open - Turn the damper motor clockwise to open the damper. NOTE Applies to integrated actuators only.
Design Properties
Static Pressure Setpoint | The desired duct static pressure (base) setpoint.
LAT Pressure Setpoint | The maximum duct static pressure setpoint that will be used during LAT override.
Property Page Text
Show Property Page Text | Check to show this microblock's value on the equipment's Properties page.
Property Page Text | You can edit the microblock description that appears on the Properties page. See "Editing Properties page text using special characters" and "Formatting a microblock property" in EIKON® Help.
BACnet configuration
Object Instance | Auto-assign - A BACnet Object ID is assigned by the system. Use specific value - (0–3999999) Assign a number that is unique within the controller.
#### Static Pressure Input Properties
Display Name | The microblock label used in the interface. You can use any characters (including spaces) in this field, except for the " character.
Description | (optional) A BACnet-visible microblock description.
Resolution | The increment by which the microblock updates the value on its output wire.
BACnet Configuration
Network Visible | Check to allow other BACnet equipment to read or change the microblock's present value. Must be checked for this microblock to generate alarms.
Object ID | Auto-assign - A BACnet Object ID is assigned by the system. Use specific value - (0–3999999) Assign a number that is unique within the controller.
COV Increment | An Analog Network Input (ANI) that references this microblock in its Address field tries to subscribe to this microblock's COV (Change of Value) service. If subscription succeeds, the ANI receives a value from this microblock only when this microblock's present value changes by at least the COV Increment. If subscription fails, the ANI reads this microblock's value at intervals specified in the ANI's Refresh Time field.
Trends
Enable Trend Log | Check to have the controller collect trend data for the microblock's present value.
Sample every ___ (hh:mm:ss) | Records the microblock's present value at this interval. EXAMPLE Type `00:10:00` to record the microblock's present value every 10 minutes.
Sample on COV (change of value) | Records the microblock’s present value only when the value changes by at least the COV Increment.
Max samples | The number of data samples the controller allocates memory for. Memory consumption is 10 bytes for each sample plus 48 bytes. For example, for 100 samples: (100 x 10 bytes) + 48 = 1048 bytes of memory The allocated memory is constant regardless of how many samples are actually recorded. If you do not enable trending, no memory is consumed. Click Reset in the WebCTRL® interface to delete all samples currently stored in the controller.
Enable Trend Historian | Check this field to archive the controller's collected trend data to the system database after every 129 data samples. NOTES You must check Enable Trend Log if you want to Enable Trend Historian. You can change Enable Trend Historian archival settings and other trend properties on the Properties page in the WebCTRL® or Field Assistant system.
Keep historical trnds for ___days | This is based on the date that the sample was read. Set this field to 0 to use the system default value.
Write to historian: Every ___ trend samples Use default (45% of Max samples) | Writes all trend data in the controller to the system database each time the controller collects the specified number of samples. You can select Every __ trend samples and enter a number greater than zero and less than the number in the Max samples field, or you can select Use default. The number of trends specified must be accumulated at least once before the historical trends can be viewed.
#### Alarms
Potential alarm source | Check to make this microblock available in the system's Alarm Sources list.
Critical | Determines the color of the system-wide alarm button when the alarm comes in if the alarm's Template field is set to Universal. = Critical = Non-critical
Category | The category you want to use to filter this microblock's alarms on the system's Alarms page > View tab.
Template | Universal - Allows your system to use the Alarm text and Return text defined in the microblock, and the Critical checkbox to determine the color of the system-wide alarm button when the alarm comes in.
Alarms
Low Limit Enable | Check to send an alarm when the microblock's present value remains below the Low Limit value for the defined Delay Seconds.
Low Limit | The value the microblock's present value must drop below to send an alarm.
High Limit Enable | Check to send an alarm when the microblock's present value remains below the Low Limit value for the defined Delay Seconds.
High Limit | The value the microblock's present value must rise above to send an alarm.
Dead Band | The amount inside the normal range by which an alarm condition must return before a return-to-normal notification is generated. EXAMPLE
Delay Seconds | The time the microblock's present value must remain in an alarm condition before the microblock sends an alarm.
Alarm Text | The message displayed on the WebCTRL® Alarms page > View tab when an alarm condition occurs. A relative path is useful for alarm messages that you will reuse in multiple WebCTRL® locations because the path is relative to the item that contains the path.
Alarm requires acknowledgment | Check to require that an operator acknowledge alarm notifications on the system's Alarms page > View tab.
Return to Normal
Return Enable | Check to send a message when an alarm condition has returned to normal.
Return Text | The message displayed on the WebCTRL® Alarms page > View tab when an alarm condition returns to normal. A relative path is useful for alarm messages that you will reuse in multiple WebCTRL® locations because the path is relative to the item that contains the path.
Return requires acknowledge | Check to require that an operator acknowledge return-to-normal notifications on the system's Alarms page > View tab.
Fault
Fault Enabled | Check to send a message when a fault condition occurs, such as a misconfigured or non-existent sensor.
#### Simulation Define the value(s) the microblock will use when you simulate the control program.
#### Tips and tricks BACnet properties The Bypass microblock is a proprietary BACnet object. If you make this object Network Visible, you can address a BACnet Analog Network Input or BACnet Analog Network Output microblock to access many of its configuration and control properties in other control programs. See BACnet object property addresses below.
#### BACnet object property addresses The Bypass microblock is a proprietary BACnet object (object type 770). The format for a BACnet address is bacnet://device/object/property@priority. EXAMPLE To set up a microblock to read the Current Value of the Duct Static Pressure from the first Bypass microblock in the same controller, use the following address. `bacnet://this/770:1/4710` In the above address, 770:1 indicates the first instance of a Bypass microblock in the controller.
BACnet property identifier # | BACnet property identifier | Description | Read/ Write
--- | --- | --- | ---
75 | PROPID_OBJECT_IDENTIFIER | BACnet ID of the BP Object | R
77 | PROPID_OBJECT_NAME | BACnet name of the BP Object | R
79 | PROPID_OBJECT_TYPE | BACnet Type | R
28 | PROPID_DESCRIPTION | BACnet Description of the BP Object | R/W
31 | PROPID_DEVICE_TYPE | BACnet Device Type | R/W
168 | PROPID_PROFILE_NAME | BACnet profile name of the object | R/W
4132 | PROPID_TAB_TECH_NAME | Name of Test and Balance Tech. | R/W
4133 | PROPID_TAB_ORG_NAME | Name of Test and Blance Company | R/W
4135 | PROPID_DISPLAY_NAME | Name of Test and Blance Company | R/W
4140 | PROPID_TAB_PARS_SEAL | BACnet Date/Time - Used to detect writes by external Test and Balance software | R/W
4121 | PROPID_LOCK_FLAGS | Binary lock bits whether to apply locks | R
4105 | PROPID_DAMPER_LOCK | Real - lock value for Damper % open | R/W
4107 | PROPID_AUTO_ZERO | Boolean - indicates completion of auto-zero | R
4108 | PROPID_TAB_MODE | Enumeration of states of damper control whle Test and Balance is performed. | R/W
4134 | PROPID_LAST_TAB_DATE | Date of last Test and Balance | R/W
4111 | PROPID_AIR_SOURCE_OBJ_ID | Airsource BACnet Object ID | R
4109 | PROPID_PAR_PRG_DEV_ID | Device ID of program containing the BP Object | R
4110 | PROPID_PAR_PRG_OBJ_ID | Program AI of program containing the BP Object | R
4123 | PROPID_SENS_CONFIG | Sensor configuration | R
4124 | PROPID_DAMP_CONFIG | Damper configuration | R
111 | PROPID_STATUS_FLAGS | BACnet status flags | R
103 | PROPID_RELIABILITY | BACnet reliability status of Object | R
4136 | PROPID_OWN_PRG_OBJ_ID | Object ID for program containing this instance | R
4125 | PROPID_FLOW_RAWPCT | Raw counts of flow sensor | R
4127 | PROPID_MOVES_TODAY | Number of damper movements today | R
4128 | PROPID_MOVES_YESTERDAY | Number of damper movements yesterday | R
4131 | PROPID_PROP_STAT_FLAGS | PROPID_PROP_STAT_FLAGS | R
117 | PROPID_UNITS | Units used by the object | R
4141 | PROPID_LOCK_FLAGS_BOOL | Boolean array of lock flags | R
4142 | PROPID_PROP_STAT_FLAGS_BOOL | Boolean array of BACnet status flags | R
4156 | APPLICATION INSTANCE | The linkage application instance used by the microblock | R/W
4703 | PROPID_BYP_VERSION | Version number of the BP microblock | R
4704 | PROPID_BYP_DSP_LOCK | Real - lock value for Duct Static Press | R
4705 | PROPID_BYP_COMMANDED_POSITION | Value of current damper commanded position | R
4706 | PROPID_BYP_AHU_MODE | Value of current AHU Mode | R
4707 | PROPID_BYP_LAT_OVERRIDE | Value of current LAT override | R
4708 | PROPID_BYP_DAMPER_MOTION | Value of current Damper Move input | R
4709 | PROPID_BYP_DAMPER | Value of current Damper Position | R
4710 | PROPID_BYP_DUCT_STATIC | Value of current Duct Static Pressure | R
4711 | PROPID_BYP_WKG_DSP | PROPID_BYP_WKG_DSP | R
4712 | PROPID_BYP_CAL_ACTIVE | Value of current Cal Active output | R
4713 | PROPID_BYP_DSP_WIRE | DSP wire current value | R
4714 | PROPID_BYP_LAT_WIRE | LAT wire current value | R
4715 | PROPID_BYP_DUCT_SP_SETPOINT | Real - Static Pressure Setpoint | R
4716 | PROPID_BYP_LAT_SETPOINT | PROPID_BYP_LAT_SETPOINT | R
4717 | PROPID_BYP_CALIBRATION_SETPT | Real - Calibration Setpoint | R
4718 | PROPID_BYP_DSP_SETPT_OVR | Real - DSP Setpoint override | R/W
4719 | PROPID_BYP_LAT_SETPT_OVR | Real - LAT Setpoint override | R/W
4720 | PROPID_BYP_CAL_SETPT_OVR | Real - Calibration Setpoint override | R/W