National Instruments NI 6602 User Manual

Also see for NI 6601: User manual Manual User manual User manual User manual

National Instruments NI 6602 User Manual Manual pdf 18 page image

Chapter 2 Device Overview© National Instruments Corporation 2-7 NI 660x User ManualEven if the Source pulses are long, the counter increments only once foreach source pulse.Normally, the counter and Counter n Internal Output signals changesynchronously to the Source signal. With duplicate count prevention, thecounter value and Counter n Internal Output signals change synchronouslyto the maximum onboard timebase.Notice that duplicate count prevention should only be used if the frequencyof the Source signal is one-fourth of the maximum onboard timebase.Enabling Duplicate Count Prevention in NI-DAQmxYou can enable duplicate count prevention in NI-DAQmx by setting theEnable Duplicate Count Prevention attribute/property. For specificinformation on finding the Enable Duplicate Count Preventionattribute/property, refer to the help file for the API you are using. Refer tothe NI-DAQmx Help for more information.When to Use Duplicate Count PreventionUse duplicate count prevention for buffered measurements that use anexternal CtrnSource signal and the frequency of the signal is less than orequal to one-fourth of the maximum onboard timebase. Use this mode ifyou are using a low frequency or you expect zero CtrnSource edgesbetween successive edges of the CtrnGate signal.You should use duplicate count prevention if the following conditions aretrue:• You are making a buffered counter input measurement.• You are using an external signal (such as PFI x) as the counter Source.• The frequency of the external source is one-fourth of the maximumonboard timebase.• You can have the counter value and output to change synchronouslywith the maximum onboard timebase.In all other cases, you should not enable duplicate count prevention.When Not to Use Duplicate Count PreventionUse duplicate counter prevention only for buffered measurements with anexternal CtrnSource signal. Do not use it when the CtrnSource signal isgreater than one-fourth of the maximum timebase.