MCC 128 & MCC 172 frequency question

[skycraper3]

Hello,

I'm using MCC 128 and MCC 172 for data acquisition and noticed frequency is not exact.

My application is continuous acquisition and split data at every hour reached, timestamps of these file is increasing constantly like
00:00:00.data
01:00:00.data
02:00:01.data
03:00:01.data
04:00:02.data...
, every file has exactly same size because it just appends data from "a_in_scan_read(frequency, timeout)" 3600 times to binary.

This application running on 2048 Hz, and I know MCC128 has cannot achieve 2048 Hz (it shows 2047.8... Hz from a_in_scan_actual_rate()), but in MCC172 shows 2048 Hz but it drift about 0.02~0.07 seconds per hour. Of course data is continuous.

These RPis has GPS source, it syncs time from GPS every minute.

Is it normal or have to handle in code?

 

Edited August 29, 2023 by skycraper3

[DAQman]

The boards will drift apart when run continuously for a length of time. If you run both for 12 hours, ideally you would get 88,473,600 input scans from each. However, the 128 will return slightly less at 88,464,960, a difference of 8640 or approximately 4.2 seconds. (check my math). The only way to overcome this is by periodically restarting them.

[DAQman]

The MCC 128 and the MCC 172 have nothing in common. The 128 uses a successive approximation converter, and the 172 uses a sigma-delta converter, and when running continuously, they will eventually drift apart. 

[skycraper3]

Hello, @JRys.

You mean both product will eventually drift if run continuously?

If so, how can I handle it or any tips?

 

Edited August 30, 2023 by skycraper3