Posts Tagged ‘transfer’
Uninterruptible Power Supply – Automatic And Static Transfer Switches
Posted by Parkzone Corsair in Power Supply on July 20th, 2010
Automatic Transfer Switches (ATS) are designed to provide resilience in power continuity planning and uninterruptible power supply (UPS) implementations below 10kVA, where UPS cannot be operated in parallel.
Static Transfer Switches are relay-based and can be used in place of PDUs (Power Distribution Units) for plug-and-play loads. Care has to be taken with such devices to ensure a single-point-of-failure is not introduced on the output side of the uninterruptible power supply. Each device is fused or protected by a circuit-breaker and should it open or rupture the load could potentially be dropped.
Automatic Transfer Switches contain two ac input power sources (A) and (B). One possible mode of operation is that Power source (A) can be supplied from the output of a UPS and (B) from a mains power supply. Another is that both (A) and (B) are supplied from two separate uninterruptible power supply outputs. Another alternative is that both are supplied from two separate mains power supplies.
When one of the power supplies fails, the load/s are automatically transferred to the second. When the two supplies are in phase with one another, the transfer is instantaneous.
In addition, an Automatic Transfer Switch can provide protection against load short—circuits, the ability to switch its output power connections on and off remotely (over a network) and load measurement locally via an LCD or built-in sub-D type communications port. ATS can also be hardwired for higher operating power.
This article was compiled using information available in The Power Protection Guide – the design, installation and operation of uninterruptible power supplies (ISBN: 9 780955 442803). By Robin Koffler and Jason Yates of Riello UPS.
Robin Koffler is the General Manager for Riello UPS Ltd the UK subsidiary of Riello UPS (RPS S.p.A) a leading European manufacturer of Uninterruptible Power Supplies and a co-author of The Power Protection Guide(ISBN 978-0-9554428-0-3)- available from Amazon.com
In The Data Stage of a USB 2.0 Control Read Transfer
Posted by Parkzone Corsair in USB on February 21st, 2010
USB 2.0 device doesn’t return an expected handshake packet during a control transfer, the host retries. On receiving no response after a (typical) total of three tries, the host notifies the software that requested the transfer and stops communicating with the endpoint until the problem is resolved.
The two retries include only those sent in response to no handshake at all. A NAK triggers a retry but doesn’t increment the error count.Control transfers use data toggles (USB 2.0) or Sequence Numbers (Super- Speed) to protect against lost data. In the Data stage of a USB 2.0 Control read transfer, on receiving the data from the device, the host normally returns ACK and then sends an OUT token packet to begin the Status stage. If the device for any reason doesn’t see the ACK returned after the transfer’s final data packet, the device must interpret a received OUT token packet as evidence that the Status stage has begun.
Devices must accept all error-free Setup packets. If a new Setup packet arrives before a previous control transfer completes, the device must abandon the previous transfer and start the new one.
A USB 2.0 device has these responsibilities for transfers on a control endpoint:
- Send ACK in response to every Setup packet received without error.
- For supported control write requests, send ACK in response to received data in the Data stage (if present) and return a ZLP in the Status stage.
- For supported control read requests, send data in response to IN token packets in the Data stage and ACK the received ZLP in the Status stage.
- For unsupported requests, return STALL in the Data or Status stage.
USB supports transfer types
Posted by Parkzone Corsair in USB on November 19th, 2009
The data throughput, or rate of transfer of application data, between a device and host is lss than the bus speed and isn’t always predictable. Some of the transmitted bits identify, synchronize, and error-check the data, and the throughput also varies with the transfer type and how busy the bus is.For time-sensitive data, USB supports transfer types that have a guaranteed rate or guaranteed maximum latency. Isochronous transfers have a guaranteed rate,where the host can request a specific number of bytes to transfer at defined intervals. The intervals can be as short as 1 ms at full speed or 125 μs at high speed and SuperSpeed.
Isochronous transfers have no error correcting, however.Interrupt transfers have error correcting and guaranteed maximum latency. The device specifies a maximum interval, and when a driver has requested a data transfer, the host allows no more than the specified interval, or maximum latency, to elapse between transfer attempts. The requested maximum interval can have a range of 10–255 ms at low speed, 1–255 ms at full speed, and 125 μs to 4.096 s at high speed and SuperSpeed.
