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By transmitting a SNAP command at the required time, all devices on the bus will sample their inputs within the
update rate set by RATE. The resulting values can then be read back in the normal way from all the devices SYSN
parameters.
Note: Instrument Explorer provides "wizards" for easy calibration of the System stage. There are two wizards, 'Sys
Calibration Auto' and 'Sys Calibration Table' these can be found under the menu item "Wizards".
Control
Shunt Calibration Commands, SCON and SCOF
The Device is fitted with a "Shunt" calibration resistor whose value is 100K.This can be switched across the bridge,
using SCON, giving an approximate change of 0.8mV/V at nominal 2.5mV/V. The command SCOF removes the
resistor from across the bridge. It is important for the user to remember to switch out the shunt calibration resistor
after calibration has been confirmed.
Digital Output, OPON and OPOF
For DSC ONLY an open collector output is available. This can be switched on using OPON and off by the command
OPOF. This output is capable of switching 100mA at 30v (TBC)
Flags
Diagnostics Flags, FLAG and STAT
All the self-diagnostics rely on the FLAG & STAT parameters, which are 16-bit integer register in which different
bits of the value represent different diagnostic warnings. FLAG is stored in EEPROM and is therefore non-volatile,
STAT is stored in RAM and reset on power-up to 0. FLAG is latching requiring reset by the user where as STAT is
non-latching showing current error status.
Latched Warning Flags (FLAG)
The flags are normally used as follows:-
FLAG is read at regular intervals by the host (like the main output value, but generally at longer intervals)
If some warnings are active, i.e. FLAG is non-zero, then the host tries to cancel the warnings found by writing
FLAG= 0
The host then notes whether the error then either remains (i.e. couldn't be cancelled), or if it disappears, or if it
re-occurs within a short time, and will take action accordingly.
The warning flags are generally latched indicators of transient error events: By resetting the register, the host both
signals that it has seen the warning, and readies the system to detect any re-occurrence (i.e. it resets the latch).
What the host should actually do with warnings depends on the type and the application: Sometimes a complete log
is kept, sometimes no checking at all is needed.
Often, some warnings can be ignored unless they recur within a short time.
Warning flags survive power-down, i.e. they are backed up in non-volatile (EEPROM) storage.
Though useful, this means that repeatedly cancelling errors which then shortly recur can wear out the device non-
volatile storage – see Chapter 3 Basic Set-up and Calibration.
34
Mantracourt Electronics Limited DCell & DSC MantraCAN User Manual
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