ODiSI 6
ODiSI 6
User’s Guide
Page 87
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Measurement Message
Contents
The Measurement Message is formatted as human readable UTF-8 text, using JSON
formatting. A carriage return plus line feed (\r\n) follows the closing curly brace of the JSON
text. A CRC-16-ANSI (0x8005) checksum (encoded as 4 hexadecimal characters) follows the
carriage return plus line feed. A NULL character follows the checksum and marks the end of
the message.
Product Name and Serial Number
The Measurement Message includes a product name and a system serial number. This
allows the client program to receive data from multiple ODiSI units. Each ODiSI will transmit
its own Metadata Message containing an identifying system serial number. The system serial
number in the Measurement Message allows the client to determine which ODiSI unit the
measurement data is from, and which Metadata Message to use to interpret the data.
Sequence Number
The Measurement Message includes a sequence number, which is incremented by the ODiSI
with each measurement transmission. This number allows the client to determine if any
measurements have been missed.
Timestamp
The Measurement Message includes a timestamp, which is split into separate JSON fields for
year, month, day, hours, minutes, seconds, and milliseconds. There is also a field to indicate
the time zone of the timestamp. The ODiSI always uses UTC timestamps, regardless of the
local time zone.
Channel Number
The Measurement Message includes a channel number, which is used to map the array of
data values to the gages defined for a particular sensor in the Metadata Measurement. The
Measurement Message does not contain gage names or units, so it is necessary to refer to
the Metadata Message to fully interpret the gage values contained in the Measurement
Message.
“Data” Element
The “data” element of the Measurement Message contains an array of decimal gage values,
formatted as human-readable ASCII text. The gage values are transmitted in the same order
in which they are defined in the metadata message. Individual gages are defined and
transmitted first, followed by segment vectors.
The measured values provided with
in the “data” array are provided as floating point values.
The JSON value
null
will be used to indicate a NaN, or “not a number” value. (Under certain
conditions, the ODiSI may not be able to calculate a strain or temperature value for a certain
gage. In these events, the ODiSI reports NaN as the gage value).
