Fluke NetDAQ 2640A, Service Manual

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NetDAQ
Service Manual
2-46
Response Packets Returned The inguard returns one response packet for the reference
junction reading if any of the measured channels is a thermocouple channel, followed by
a response packet for each channel measured, returned in ascending channel order,
followed by a response packet for each housekeeping reading specified by the scan
command.
Response Packet Format Each response packet for a Perform Scan command consists
of a floating-point number representing the measurement value, the range used to take
the measurement, the channel number, and the checksum. The floating-point format used
is ANSI/IEEE Std 754-1975 single-precision. Positive and negative overload conditions
cause a value of PLUS_OVLD_VAL (0x7f800000) and MINUS_OVLD_VAL
(0xff800000), respectively, to be returned. A frequency channel whose input frequency
is too low to measure returns 0 Hz. A channel with an open-thermocouple condition
causes the value of OTC_VAL (0x7fc00000) to be returned. The inguard waits until it
has completed all measurement activity associated with a particular scan before
beginning the transmission of the response packets for that scan to the outguard.
The floating-point value returned has a nominal range of -3.0 to +3.0. The outguard must
scale this according to the channel function and range to produce the correct volts or
ohms. For most ranges, a full-range value is returned as +3.0. For example, on the 300
ohm range, +3.0 represents 300 ohms. For the 90 mV and 750 mV ranges, however, +3.0
represents 93.26 mV and 0.746083V, respectively. Also, frequency readings always
return the actual frequency measured and do not require range-scaling by the outguard.
Perform Self-Test 2-81.
The Command Packet tells the A/D to perform all self tests. Response Packets Returned
always returns a single response packet. The Response Packet Format provides the
following:
•
A/D self-test result, pass or fail.
•
Zero Offset self-test result, pass or fail.
•
Reference Balance self-test result, pass or fail.
•
Ohms Overload self-test result, pass or fail.
•
Open Thermocouple self-test result, pass or fail.
•
Checksum
Return Main Firmware Version 2-82.
This Command Packet requests version number of the inguard main firmware and
always returns a single response packet.
Response Packet Format The response consists of five ASCII characters (plus the
checksum byte), in the form txxyy, where t is “F” for FFE (2645A) software and “P” for
the PFE (2640A); xx are the two digits of the major version number, and yy are the two
digits of the minor version number (there is an implicit decimal point between the two).
Note that constraining the bytes to be ASCII characters causes the most significant bit of
each character to be a 0, making the response packet always distinguishable from a
NAK.