Yokogawa PC-Based MX100 - Manual (Page 7)

IM MX190-02E

With the Extended API
The figure below shows the conditions when the extended API retrieves measured data
(2 and 3 in the "Program Flow" table). When specifying instantaneous values, the most
recent data becomes "Current."
Second time
FIFO buffer
(MX100)
FIFO buffer
(MX100)
Current
(Measurement
point)
(Most recent data)
First time
Current
(Previous
Current + 1)
To advance to a measurement point, use the measured data retrieval functions (status
transition functions). To read Current data, use the appropriate retrieval functions.
For information about the measured data retrieval functions (status transition functions)
and the retrieval functions, see the referring pages in the table below from the API for the
MX100/DARWIN user's manual (IM MX190-01E). See the appendix for the locations of
the program examples.
Programming
Language Reference
Retrieval functions of the status
transition functions
Retrieval functions
Visual C++ Page 12-8, "Retrieval Functions" Page 12-9
Visual C Page 13-6, "Retrieval Functions" Page 13-7
Visual Basic Page 14-6, "Retrieval Functions" Page 14-7
Visual Basic .NET Page 15-6, "Retrieval Functions" Page 15-7
C# Page 16-6, "Retrieval Functions" Page 16-7
Data Acquisition with Instantaneous Values
Data acquisition with instantaneous values involves retrieving the most recent data from
the FIFO buffer. The API can access the MX100's measured data in as fast as 100 ms.
Thus, instantaneous values are retrieved every 100 ms at best. To retrieve data at faster
measurement intervals, the FIFO number must be specified.
Starting and Stopping FIFO
FIFO must be started before retrieving data from the MX100. When FIFO is started by
the API, all FIFOs are started, and when stopped, all FIFOs are stopped.
Notes When Retrieving Data
The PC must access the MX100 and read out the data before the buffer becomes full.
The size of the three FIFO buffers combined is 2 MB. For example, when acquiring
60 channels of data at a measurement interval of 10 ms, the buffer becomes full in
approximately 60 seconds.
* When the buffer becomes full, the MX100 overwrites old data
with new starting from the top. Therefore, the PC must retrieve the data from the MX100
at intervals of less than 60 seconds. Determine the actual retrieval interval based on your
application.
* For instructions on how to calculate the time required to fill the buffer, see appendix 3,
"Calculation of the MX100 Timeout Value" in the API for the MX100/DARWIN user's manual
(IM MX190-01E).
If access is not gained in approximately 3 minutes, the MX100 breaks off communications.