Measurement Computing LogBook Series - Manual (Page 90)

6-2 GPS and Serial Device Data Collection 958396 LogBook User’s Manual
Serial Input Fundamentals
Every LogBook input and output is called a channel. When an input channel is enabled, the LogBook will sample
and save it at the specified frequency. To collect and save numeric data from serial devices, a serial channel must
be defined. Each serial channel defines a single number embedded in the ASCII serial input string sourced by the
serial device. Each serial channel has an associated format string that provides the parsing and converting
instructions to the LogBook. Up to 16 serial channels can be defined within the LogView software application.
Terms
Serial channel
A serial channel is a LogBook data element, like an analog input channel, that can be
collected and stored with the other analog and digital input data. A serial channel defines
a single numeric field within the serial data stream sourced by the serial device.
Serial input string A serial input string is the ASCII data being transmitted by the serial device. Typically,
the serial input string contains several numeric and character fields, and is terminated by
carriage return (CR) and/or line feed (LF) characters.
Format string A format string is a user-created character string that contains the instructions necessary
for the LogBook to parse out the desired field in the serial input string.
Capabilities and Limitations
Interface type RS-232 devices.
Data types The device must supply an ASCII sentence, an ASCII data string terminated
by a CR and/or LF. The device must transmit its data without any inducement.
Devices that require a data request command from the controller are not supported.
Serial input string size The size of a terminated sentence cannot exceed 255 characters.
Number types
Integers (+/-32,768), floats (3.4E+/-38 with 6 digits of decimal precision), and character
(+/-128) types are accepted.
Serial channel usage Like all other input channels in the LogBook system, serial channels can be used in
equations defining calculated channels and/or used in the definition of the
trigger or stop events.
Serial baud rate 1200, 2400, 4800, 9600, 38400, 57600, 115200.
GPS port General serial devices can be attached to either port 1 and/or 2, but a GPS device can
only be attached to Port 1.
Synchronicity The LogBook’s analog and digital input channels are synchronously sampled at the
specified rate(s) using an internal or externally supplied sample clock. Serial devices
provide data to the LogBook asynchronously to its sample clock. When a serial input
string is parsed and converted, its value is placed in temporary storage. When the sample
clock fires, the current value in temporary storage is scanned along with the analog and
digital input channels and written to the LogBook’s non-volatile PC-Card memory.
If the sample rate associated with the serial channel is slow relative to the transmission
speed of the serial device, the temporary storage may be updated several times between
recorded samples. If the sample rate of the associated serial channel is fast relative to the
transmission speed of the serial device, the temporary storage may be sampled and stored
many times without any new updates from the serial device.
Data validity When the system is first armed the serial channel data may be invalid for an
undetermined number of scans. Until the serial device provides that which is required by
the serial channel definition, the associated serial channel will be invalid. For high
sample rates, many scans may be executed before valid data is present on the serial
channels.