Operator`s manual
17 Signametrics
Note: All of the controls described below correspond to their respective software function, which can be
invoked within your control software or as objects in a visual programming environment. The software
command language provides a powerful set of capabilities. Some of the functions are not included in the
control panel, but are in the software.
DC/AC This function switches between DC and AC. This is applicable for the Voltage and Current
DMM functions.
Relative This is the Relative function. When activated, the last reading is stored and subtracted from all
subsequent readings. This is a very important function when making low-level DCV measurements, or in
2W. For example, when using 2W, you can null out lead resistance by shorting the leads together and
clicking on Relative. When making low level DC voltage measurements (e.g., in the V region), first
apply a copper short to the V, + & - input terminals, allow the reading to stabilize for a few seconds,
and click on Relative. This will correct for any internal offsets. The Relative button can also be used in
the Percent and dB deviation displays (shown below), which are activated using the T
ools in the top
menu.
Rate Box: Controls the DMM Measurement rate. As rate decreases, the measurement noise decreases.
Also consider the power line frequency (50/60 Hz) of operation when setting it, as certain rates have
better noise rejection at either 50 or 60 Hz. (See “Specifications” for details.). When measuring VAC
values, there is no point setting the Rate to a value greater than 2rps.
Range: Can be set to Autorange or manual by clicking on the appropriate range in the lower part of the
Windows panel. Autoranging is best used for bench top application. Autorange is not recommended
for automated test applications due to the uncertainty of the DMM range, as well as the extra time for
range changes. Locking a range is highly recommended when operating in an automated test system,
especially to speed up measurements. Another reason to lock a range is to control the input impedance in
DCV. The 240 mV and 2.4 V ranges have virtually infinite input impedance, while the 24 V and 240 V
ranges have 10 M input impedance.
S_Cal: This function is the System Calibration that corrects for internal gain, scale factor and zero
errors. The DMM does this by alternatively selecting its local DC reference and a zero input. It is
required at least once every day to meet the accuracy specifications. It is recommended that you also
perform this function whenever the external environment changes (e.g. the temperature in your work
environment changes by more than 5C. This function takes a few seconds to perform. Disconnect all
leads to the DMM before doing this operation. Keep in mind that this is not a substitute for periodic
calibration, which must be performed with external standards.