11
Signametrics
2.7 Measurement Rates Control
Use DMMSetRate() using the following codes.
Power line Rejection
Rate
(Readings/sec)
Symbol Code
50Hz 60Hz 400Hz
0.5
RATE_p5
0
1 RATE_1
1
2 RATE_2
2
3 RATE_3
3
7 RATE_7
7
14 RATE_14
14
27 RATE_27
27
50 RATE_50
50
90 RATE_90
90
170 RATE_170
170
250 RATE_250
250
2.8 Accuracy Notes
Important: a
ll accuracy specifications for DCV, Resistance, DCI, ACV, and ACI apply for the time periods shown
in the respective specification tables. To meet these specifications, Self Calibration must be performed once a day or
as indicated in the specification table. This is a simple software operation that takes a few seconds. It can be
performed by calling Windows command DMMCal(), or selecting S-Cal in the Control Panel.
These products are capable of continuous measurement as well as data transfer rates of up to 250 readings per
second (rps). In general, to achieve 6-1/2 Digits of resolution, the rate should be set to 2rps or lower.
Since the DMM is powered via a USB calbe (AM/BM 6’ cable), it is important to make sure it gets the
required 5V supply. Using the right USB cable is very important. Make sure this cable has a 24 AWG
wires for power supply, indicated by marking on the cable such as 28/1P + 24/2C. Be aware that there are
a lot of cables which are marked 28/1P + 28/2C. These have high resistance, and will not be adequate.
Another issue can be with powered USB hubs. Some of the lower quality units can have upwords of 8V
rather than the required 5V +/-5%. On initialization (DMMInint) the DMM measures its internal supply
voltage and returnes an error or warning code if the power is inadequate. See DMMGetSupplyV function.
