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The Johnson Metasys® option board is designed to enable error free communications between the VTAC 7 Variable Speed Drive and the N2 Building Automation Control system. This internally-mounted option board can be programmed for either monitoring or full control via the network allowing users to customize drives in HVAC systems. No functionality or control option is sacrificed when installing this card on a fan or pump drive. You decide the appropriate level of network control or monitoring.
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Function
Johnson Metasys is a RS485 control network designed specifically for HVAC building automation applications. Data is transmitted and received over a dedicated set of wires running throughout the building. Each device on this network is assigned an address and can be accessed by the host Johnson controller. Because the Variable Speed Drive is placed on this high level N2 bus directly, no additional hardware or wiring is necessary. Users can choose the type of information passed over this bus as dictated by the application. Safety interlocks and critical drive operations such as smoke purge, can be hard wired external to the communication bus for added system fault protection. Cost savings are realized during system installation and when adding future software based upgrades.
Standard Features
- Control: Simple drive "start/stop", "reset fault", "forward/reverse", and "clear error log" commands are set in a single binary output register from the host Metasys system. Speed reference to the drive is set in an analog output register with a value from 0 to 4095 (12 bit) linearly scaled between user settings of Min and Max speed. Since all signals are digital, very precise control can be achieved without the use of 4-20 ma or 0-10 Volt references. If communication is lost, you may program the drive to follow the last reference, run at a pre-set speed, or coast to stop and set a fault bit indicating loss of host communications.
- Tuning: Many systems change over time due to variations in temperature, humidity, pressure, and operating conditions. Access to tuning parameters in the drive allows for adaptation to changes in the system. Min and Max speeds, as well as Acceleration and Deceleration times, may be adjusted over the network to compensate for system requirements involving control loops. To speed data transfer on the network, access to these tuning" parameters can be selected only when changes are downloaded to the drive.
- Monitoring: Even if the drive is controlled from traditional hardwired inputs or the keypad, monitoring of the drive is possible over the network. Feedbacks such as drive speed, motor current, motor voltage and output power can be monitored and used for data trending and energy management purposes. If a fault occurs, the exact cause of the drive trip is displayed in a Metasys binary input register. Complete drive status, including any mapped digital signals such as ByPass running, is transmitted back to the Johnson system for easy diagnostic analysis. Troubleshooting and maintenance is greatly enhanced since this information not only indicates a drive is down, but also transmits the exact fault speeding corrective action.
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Configurations: Setting up the VTAC 7 drive for network communications is simple via a single parameter. When the option card is installed and the control source is selected as the network, the card becomes active. If the network is used only for monitoring, and control is hard wired through an AHU controller or other discrete device, once the card is installed it is active automatically. No special programming or software is required to operate over the network.
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