SCANGetStepTime()
to read it. When enabled during Auto Scan, the trigger output signal will have a period equal
to the Step Time, and depending on trigger polarity, a negative or positive pulse corresponding to the Actuation
time. The trigger can be used to provide means for triggering external devices with the desired delay. For example,
consider a case where the Actuation time has been set to 50ms, but the relays actually settle within 10ms. In this
scenario, additionally consider a Step time that has been left at its default value of 100ms, along with a trigger
output that has been enabled and set for positive sense. With these parameters, the rising edge of the trigger output
is delayed by 40ms (50ms – 10ms) from the time the relays are closed and settled, and the scanning speed is 10
channels per second (1/100ms).
Figure 4-11. Step Time and Actuation Time parameters relations.
4.2.14 Thermocouple Temperature Measurements
When making thermocouple temperature measurements, it is important to use the SMX40T. It is isothermal,
meaning that an even temperature is maintained across all terminals. The SMX40T has an active temperature sensor.
It is connected to the channel 35 (D-bus), and provides for cold junction (or reference junctions) temperature
measurement. When using the SMX40T this channel is not available for anything else. By configuring the 4032 to
ColdJunction
;
SCANSetConfig(ColdJunction),
channel 35 gets connected to the A-Bus terminals, and can be
measured by a Digital Multimeter. Channel 35 may also be selected while the 4032 is configured for
TwoWire
, by
an explicit selection;
SCANSelectChannel(
35
).
The temperature of the Isothermal Block, or the, or the temperature where the thermocouples are
connected, is required in calculating the thermocouple temperature. Most of the Signametrics Digital
Multimeters have a measurement function that is capable of both, measuring and calculating the sensor
temperature, as well as linearizing thermocouple measurements. Following the selection of the sensor;
SCANSetConfig(ColdJunction
) u
se the
DMMReadCJTemp
of the 2040 or 2060 series DMMs to perform
the Cold Junction temperature measurement
. Once measured, these DMMs store this temperature value for
subsequent thermocouple measurements.
4.3 Polled Type Operations
Since the Scanner has it’s own controller, it is capable of processing operations, such as selecting a channels or
executing a long test procedure, without help from the PC. For instance, when the
SCANSelectChannel()
function
is issued, the DLL waits for the completion of the operation. It actually waits for the Scanner to complete the
operation. In response to the command the Scanner opens the appropriate channels, closes the selected channel, and
then waits for Actuation time prior to responding with ‘operation complete’ to the PC (DLL). When using the
polled
version of the above command,
SCANSelectChannelCmd()
, no waiting takes place. The command is sent
to the Scanner and the driver (DLL) does not wait for response
.
A test program may take advantage of this. It can
issue the
polled
command, than perform various other tasks, such as setting a DMM range, then check the Scanner
for completion of the polled command by using
SCANReady().
When
the last command returns
TRUE
, it means
that the Scanner is ready to accept a new command, and in the case of channel selection, the selected channel is
closed and settled. If
SCANReady()
returns
TRUE
, it should not be used again until the next polled command is
issued.
The following is a list of all
polled
functions:
SCANSelectChannelCmd()
,
SCANAutoScan()
,
SCANTrigAutoScan()
,
SCANTrigScan()
,
SCANStepCmd()
and
SCANCleanRelays()
.
4.4 Interfacing to the SMX2040 series 6-1/2 Digit PXI DMM
The SMX4030 series Scanners are designed to interface to the SMX2040, SMX2042, and SMX2044
Digital Multimeters. The following section describes both, the hardware interface and the software
functions used to implement a synchronized operation.
25
Signametrics
