Operator`s manual

TRIG / GUARD Both the Trigger and Guard functions are at the DIN-7 connector. This group of pins includes
the positive and negative hardware trigger input lines and the two SM2044 Guarded Measurement Force and Sense
signals. The external trigger initiates reading(s) into the onboard buffer, and the 6W guard signals facilitate in-
circuit resistor measurements by means of isolating a loading node. The DIN-7 plug can be ordered from
Signametrics and is also available at many electronic hardware distributors. The connector is generically referred to
as a mini DIN-7 male. The trigger signal should be in the range of 3 V to 12 V peak. The two 6W guard signals
should never have more than 5 V peak across them.
Warning! The DIN connector pins are protected to a maximum of 35 V with respect to the PC chassis and
any other DMM terminal. Do not apply any voltages greater than 35 V to the DIN connector pins. Violating
this limit may result in personal injury and/or permanent damage to the DMM.
DIN-7, Pin number Function
7 External Trigger, Positive terminal
4 External Trigger, Negative terminal
1 Guard Source (SM2044)
6 Guard Sense (SM2044)
DIN-7 Connector Pin Description, view from bracket side.
3.5 Starting the Control Panel
You can verify the installation and gain familiarity with the DMM by exercising its measurement functions using
the Windows based Control Panel. To run the control panel, double click the “SM2044.EXE”. If you do not hear
the relays click, it is most likely due to an installation error. Another possible source for an error is that the
SM40CAL.DAT file does not correspond to the installed DMM.
The Control Panel is operated with a mouse. All functions are accessed using the left mouse button. When the
DMM is operated at very slow reading rates, you may have to hold down the left mouse button longer than usual for
the program to acknowledge the mouse click.
Note: The SM2040 front panel powers up in DCV, 2 readings per second, 330 V range. If the DMM is operated in
Autorange, with an open input, you may hear the SM2040 relays clicking every few seconds, as a range change
occurs. This is perfectly normal with ultra high impedance DMMs such as the SM2040. This phenomenon is
caused by the virtually infinite input impedance of the 330 mV and 3.3V DC ranges. On these ranges, an open input
will read whatever charge is associated with the signal conditioning of the DMM. As this electrical charge
changes, the SM2040 will change ranges, causing the relay clicking. This is normal.
21 Signametrics