Signametrics Corporation SM4020 Operator'S Manual Download Page 24

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measured using the

SCANTestConfigRelay()

function and the channel relays using the

SCANTestChannelRelay()

function. Set the Actuation time using

SCANSetActuationTime ()

and read it with

the

SCANGetActuationTime()

function. The SM4000 family of Scanners have a special active Release (drop-out

time) circuit, which forces all relays to release much faster than operate. For this reason, the Actuation time also
includes the release of a currently closed channel, in a break before make multiplexing. In configurations such as
the

TwoWire, FourWire, SixWire, TwoGroups,

and

FourGroups

, the Actuation time includes both the release and

operate processes. When enabled, the trigger output signal corresponds to the Actuation time. The trigger polarity
may be set positive or negative to provide means for triggering external devices when the switching is settled.
Further, the Actuation time maybe set to a value higher than necessary for relay actuation to provide delayed trigger.
Actuation time may be set to a value between 1ms to 850ms.

4.2.13 Setting Step Time Parameter

This parameter is the Auto Scan period, or step time. It maybe set to a value between 1ms to 850ms. On power up, it
defaults to 100ms. It is the channel to channel scan time in Auto Scan. Use

SCANSetStepTime()

to set it and

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

With the active Isothermal terminal block option, it is possible to measure temperture using
thermocouples. The active Isothermal block has a temperature sensor on the board, which can be
measured using the Signametrics SM2040 series DMM with Thermocouple option. Several additional
measurement functions included with this option allow both, reference junction temperature measurement
and linearization of several common Thermocouple types. The junction temperature is measured by
setting the Scanner to the Universal configuration and closing the AtoA DtoA and DtoD relays. This
allows the measurement of the D-bus, which is connected, on the terminal block, to the temperature
sensor of the active isothermal terminal block.

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 PC (DLL) does not wait for response

A test program may take advantage of this. It can issue

the

polled

command, then perform various other tasks, such as setting a DMM range, then check the Scanner for

completion of the polled command by using

SCANReady().

When