10.3.1 First notch frequency
The first notch frequency (
f
N1
) determines the lowest frequency that will be eliminated, or
notched out, by a sinc filter. This filter notches out frequencies at integer multiples of
f
N1
by
averaging for a time equal to 1/
f
N1
. Thus, lower first notch frequencies result in longer
measurement times. Any value between 2.5 Hz and 30 kHz can be entered, but the value will be
rounded to the closest of 16 frequency options, with the midway point rounding up. The options
for the first notch frequency are shown in
Common options for filtering noise are:
l
30000 – Performs a 0.0333 millisecond integration (for fast measurements)
l
60 – Performs a 16.67 millisecond integration (filters 60 Hz noise)
l
50 – Performs a 20 millisecond integration (filters 50 Hz noise)
10.3.2 Panel temperature
Each terminal strip has a panel temperature thermistor (Measurement Specialties 10K3A1A)
located just under its center-point. The VOLT 108 includes two panel-temperature thermistors,
and the VOLT 116 includes four. The thermistor has an interchangeability specification of 0.1 °C
for temperatures between 0 and 70 °C. Below freezing and at higher temperatures, this
specification is degraded. Combined with possible errors in the completion-resistor measurement
and the Steinhart and Hart equation used to calculate the temperature from resistance, the
accuracy of panel temperature is estimated at ±0.1 °C over 0 to 40 °C, ±0.3 °C from –25 to 50 °C,
and ±0.8 °C from –55 to 85 °C.
The panel temperature can be measured with the
CDM_PanelTemp()
instruction, where each
thermistor is numbered as shown in the following figure. In thermocouple measurements, using
the panel temperature for the thermocouple-wiring strip will result in more accurate
measurements.
CDM_TCComp()
automatically measures the nearest panel temperature.
(p. 46), shows how to use this instruction. Short Cut automatically uses the proper
reference.
VOLT 100 series
32
