Data acquisition with highly accurate GPS time stamping (hh:mm:ss:sss UT)

A research group has developed a data acquisition system dedicated to daily observations of solar phenomena at radio waves using high time resolution (5-100 ms).
First, the analog signal from the antenna (1000-2500 MHz) is sent to a spectrum analyzer (HP8559-A). After that, the analog signal is digitized during 5 minutes in a NI USB-6009 device connected to the PC, before to be stored in a file. By that time, other acquisition data cycle is restarted and so on up to the end of day.
However, we need timestamp (UTC) the solar data at the beginning and end of each sample of 5 milliseconds, during all acquisition process, in order to have the UTC time information of recorded solar events. So, a time resolution of at least 1 ms is required.
A software permit us to read recorded data and visualize corresponding spectra during last 5 minutes. However, we need UTC time information in the format hh:mm:ss.sss UT. Then, UTC millisecond is important for us, but not available yet.
To solve this problem, we are searching for a high accuracy timing GPS receiver (on the order of microseconds or nanoseconds), with at least three significant digits of precision (UT time in milliseconds) and which give us the UTC signal at least each 5 milliseconds or even better (1 ms). However, most GPS receivers only outputs 1 PPS (Pulse Per Second = 1000 millisecond).
Then, we are open to a better addressing on how to solve this problem !!
We know that GPS time synchronization with PXI-6608 can be used to precisely timestamp data acquisition, but we have to solve this problem with a lower cost. Also, we require a PCI interfacing instead of PXI.
Do we have to use a timer card? How do we use a timer, GPS and USB-6009 to timestamp data acquisition? Does the NI PCI-6602 solve the problem?
Obs:
The data acquisition software was developed in C++ Builder to run on a PC (Pentium III 2 GHz) under Windows XP environment. We used the NI-DAQmxBase driver to sample the signal from the NI USB-6009.
We are sure your expertise can help us on this matter.
Regards,

I better explain my problem in the thread How to timestamp continuous analog data acquisition using USB-6009 and GPS timing board?
We are considering to use the PCI-1588 or a GPS timing board (low-profile slot too), but I´m not sure that the USB-6009 can be used to solve the problem.
How to syncronize the data acquisition and timestamps using USB-6009 and PCI-1588 with external GPS?
In other thread I would appreciate any suggestions for GPS timing board and PCI-1588 too.
Regards,
Lilian

Similar Messages

High-speed aquisition time stamp

I am using traditional NI-DAQ with a 6071E board and acquiring data at very high rates using AquireWaveforms.VI I want to save this data in a text file with either a column of time first or even a column of time before each channel (anywhere from 1-64 channels). Because I am acquiring at such high rates, I suppose I want to be able to extract timing data from the Hardware since I'm not looping and any software timing wouldn't be accurate. Also, if at all possible I want to be able to have the time for each measurement from each channel so I can include the phase shift that comes with multiplexing. Is any of this possible? I really need resolution much better than 1 second. at least to the millisecond, but I am looking for even bette
r than this.
Thanks so much,
Rick

The waveform carries a DT (delta Time) component.
Use the GET WAVEFORM COMPONENTS function to extract the DT. That should be the actual dT used, not necessarily the rate you asked for.
If you have a DT number, you create the array with a FOR loop:
For I = 0 to NSamples-1
Time[i] = i * DT
As far as the inter-channel time, the minimum value is a property of the card, but it's also controlled by software: LV can extend it.
I don't know about the express VIs: I never use them. But the original AI CLOCK CONFIG, has an input where you can specify it.
If that doesn't work, and you have access to some test equipment, you can find it out for yourself:
Set up a ramp generator for 0.0 - 1.0 V at 1000 Hz.
This means the voltage is
changing 1 volt per mSec.
This means the voltage is changing 1 mV per uSec.
Wire the ramp generator to channels 0, and 10.
Perform a DAQ operation, with all channels 0-10 active.
Pick out a portion of the waveform, where the voltage is increasing on all channels (exclude the drop at cycle's end). Ignore channels 1-9.
Subtract the channel 10 array from the channel 0 array.
Average the result array and divide the average by 10.
The average value, in mV, is the channel delay time, in uSec.
By comparing channels 0 and 10, you're measuring 10 intervals, not one, so you're more accurate.
Steve Bird
Culverson Software - Elegant software that is a pleasure to use.
Culverson.com
Blog for (mostly LabVIEW) programmers: Tips And Tricks

Data acquisition with daq card 6533

Hi all,
i need to develop a c++ (visual studio .net, no measurement studio)
program that performs data acquisition at a sampling rate of 10Khz
using a windows xp laptop and the daq6533 card.
The program must sample 8 digital signals. Each signal has a limited
time duration, say a few seconds, and acquisition should start on the
first rising edge of a signal, and terminate on user input. Browsing
through the code provided with the driver, i found the examples in the
cdio folder. It seems to me they almost do what i actually need.
Unfortunately, many of the functions used there are not supported by
the 6533 card, in particular the GPCTR_* family. I've read somewhere
else that this card does not have an hardware counter, is that exact?
I'm a beginner in this field, so i don't know what are possible alternative solution to my problem (if any).
Thanks for any help.
walter

Thanks for your reply.
I don't know actually whether i need to use counter-related functions. My problem is the following:
I need to sample 8 digital signals with a frequency of 10khz. Every signal have a duration of a few seconds in time, and they come from sensors attached to a train's railway. Acquisition begins on the first rising edge of a signal (which coincide with the passage of the train), and end with user input (which should be after the train has passed).
It would be of great help if you can point me to a relevant example, or give me some basic guidelines on our to proceed. If you need more information, please just ask.
thank you very much.
walter

Data-acquisition with NI 6036E DAQ card & GPIB using an external trigger

Hi all,
I hope somebody could give me some help with the following and answer some questions:
Simple system description:
Labview 6.1
PCI-GPIB card
6036E DAQ card
In my system, I am using an external analog trigger signal (A) for continuous data-acquisition. Characteristics of the analog trigger signal (A) are: ~40 Hz, signal height +1.48V, triggered by rising edge (the analog trigger signal (A) could be changed to a TTL signal). Each data-acquisition is done within ~1.0 ms after the rising edge of the trigger pulse. The timing of the data-acquisition and analyzing procedure is controlled by execution in a sequence structure placed in a loop.
Now, I connected a power meter to the system, to measure the laser power during the data-acquisition. The power meter has two options to provide the laser power data:
a) via analog signal output (voltage corresponds to laser power in watts)
b) via GPIB (direct output reading of laser power in watts).
Problem:
During a certain point in my data-acquisition sequence structure (defined by a frame), I want to use the next occuring analog trigger signal (A) to acquire 1 value from the power meter.
How do I do this in Labview programming for the following two situations?
a) If I connect the analog output from the power meter to an analog input channel of the 6036E DAQ card. The analog trigger (A) would be connected to a second analog input channel (In case the analog trigger signal (A) is changed to a TTL signal it would be connected to the PFI0/Trig input pin on the DAQ card).
b) If I use the GPIB connection of the power meter. The analog trigger (A) would be connected to a second analog input channel (In case the analog trigger signal (A) is changed to a TTL signal it would be connected to the PFI0/Trig input pin on the DAQ card).
An other possibility would be to trigger the power meter directly, so it outputs constantly power meter values at ~40 Hz. How could I than acquire 1 power meter value (at a certain time im my sequence structure) via analog input at DAQ card or GPIB?
Additional questions:
How do I configure the PFI0/Trig pin on the 6036E DAQ board individually as an INPUT?
How do I use an analog trigger signal (A) as counting signal for a loop, or as an activation signal for a sequence structure which includes GPIB commands?
It would be very nice if somebody could give me some help.
Kind regards,
beam

Hi beam,
I just want to verify that I understand your situation correctly:
An external trigger signal (A) is wired to one of your input channels (e.g. CH0) to trigger data acquisition of a second channel (e.g. CH1). Your power meter is connected to an analog input channel, which you would like to trigger with a certain rising edge at some of your sequence structure.
Problem:
During a certain point in my data-acquisition sequence structure (defined by a frame), I want to use the next occuring analog trigger signal (A) to acquire 1 value from the power meter.
How do I do this in Labview programming for the following two situations?
a) If I connect the analog output from the power meter to an analog input channel of the 6036E DAQ card. The analog trigger (A) would be connected to a second analog input channel (In case the analog trigger signal (A) is changed to a TTL signal it would be connected to the PFI0/Trig input pin on the DAQ card).
If a task has been configured to acquire signal from one analog channel, it's not possible to run a second analog input task or to add a second channel on the fly. You had mentioned that it's possible to read from the instrument through GPIB. Is it possible to perform a software trigger such that at a certain frame of your structure, when the trigger signal A reaches voltage "x", a GPIB command is written to your power meter to query a measurement reading?
Additional questions:
How do I configure the PFI0/Trig pin on the 6036E DAQ board individually as an INPUT?
You do not need to explicitly configure the PFI0 line as an input. If you want to use it as an input such that it acts as an analog trigger, simply wire the trigger signal to this pin. When configuring the trigger in your software, specify PFI0 as the trigger source.
How do I use an analog trigger signal (A) as counting signal for a loop, or as an activation signal for a sequence structure which includes GPIB commands?
You can try using the Limit VI to find out when the trigger signal reaches a certain level, and count how many times this level is reached. Similarly, you can use this as the condition to execute GPIB commands.
Hope this helps,
Lesley

GPS time stamp

Hi..
I am using NAVILOCK GPS tool for work related to the laser radar. I
wrote a simple vi which writes out the time stamp in a fashion of
12:13:21 (UTC,hh:mm:ss). But I need to have second information more
precisely as we are aquring our data at the time interval of 0.33
second. So I need to have the time stamp as 12:13:2133 and so on...
Pls post your reply.
Sandy

This thread continues here.
Ingo Schumacher
Systems Engineer Sound&VibrationNational Instruments Germany

Data acquisition on the basis of time

Hi everyone,
I want to acquire the radial run-out (radial small displacement) of a rotating spindle using a capacitive sensor. To do so I will use the LabView v. 7.1. The PCI-6036E card from National Instruments (NI) will be utilized for data acquisition. The spindle turns at 100 rpm and a rotational incremental encoder is fixed at rear of spindle. This encoder provides an index digital pulse per revolution. This pulse should be used to start and finish the sampling process. I want to sample on the basis of time, by means of sampling rate of the card (Ksamples/s). So, let us suppose that I want to acquire 500 data/rev. The spindle takes 0.6 sec to complete one revolution. Thus, the required sampling rate is Fs = 500 samples/0.6 s = 833 samples/s. So, I should set the VI in LabView so that it samples only 833 data/s. Therefore, I will have to reduce the sampling rate of the analog-input channels in use. For example, let us suppose that the card provides 100 Ks/s when operating in multiple channels. Let us admit that there are 4 analog-input channels in use. So, the scan rate per channel is 25 Ks/s. This is too much for this application. I only need 833 samples/s. So, I should program the VI so that the card provides that required sample rate. As said earlier, I need to start and end the sampling process at the same point. Thus, to do that the index pulse of the encoder will be used. Also, I want to sample during 5 consecutive revolutions of the spindle. So, by means of a loop in VI, I should count the index pulse of encoder until the number of pulses be equal to 5 (= number of revolutions). At this instant, the sampling process should be stopped. Note: 1) the sampled data should be put in a buffer. After the sampling process is finished, this data should be saved in a file of LabView; 2) In fact, the data acquired by the sensor are voltage analog input. Questions:1) Could you make a VI for this problem, please? Note: you can use the DAQ ASSISTANT EXPRESS VI or DAQmx TASK NAME CONTROL method2) What should I do to stop the data acquisition at the end of 5 revolutions using the index pulse of encoder?3) Could you send examples (VIs) similar to my problem above? In anticipation, thank you very much for any help. My e-mail: [email protected]
Bruce

duplicate post
Continue in other thread
Message Edited by smercurio_fc on 11-14-2008 09:10 AM

Continuous data acquisition and analysis in real time

Hi all,
This is a VI for the continous acquisition of an ECG signal. As far as I understand the DAQmx Analog read VI needs to be placed inside a while loop so it can acquire the data continously, I need to perform filtering and analysis of the waveform in real time. The way I set up the block diagram means that the data stays int the while loop, and as far as I know the data will be transfered out through the data tunnels once the loop finishes executing, clearly this is not real time data processing.
The only way I can think of fixing this problem is by placing another while loop that covers the filtering the stage VIs and using some sort of shift registeing to pass the data to the second loop. My questions is whether or not this would introduce some sort of delay, and wether or not this would be considered to be real time processing. Would it be better to place all the VIs (aquicition and filtering) inside one while loop? or is this bad programming practice. Other functions that I need to perform is to save the data i na file but only when the user wants to do so.
Any advice would be appriciated.
Solved!
Go to Solution.

You have two options:
A. As you mentioned, you can place code inside your current while loop to do the processing. If you are clever, you won't need to place another while loop inside your existing one (nested loops). But that totally depends on the type of processing you are doing.
B. Create a second parallel loop to do the processing. This would decouple the processes to ensure that the processing does not hinder your acquisition. See here for more info.
Your choice really depends on the processing that you plan to perform. If it is processor-intensive, it might introduce delays as you mentioned.
I would reccomend you first try to place everything in the first loop, and see if your DAQ buffer overflows (you can monitor the buffer backlog while its running). If so, then you should decouple the processes into separate loops.
Regarding whether or not "this would be considered to be real time processing" is a loaded question. Most people on these forums will say that your system will NEVER be real-time because you are using a desktop PC to perform the processing (note: I am assuming this is code running on a laptop or desktop?). It is not a deterministic system and your data is already "old" by the time it exits your DAQ buffer. But the answer to your question really depends on how you define "real-time processing". Many lay-people will define it as the processing of "live data" ... but what is "live data"?

Data acquisition with time stamp

Hi I'm using NI DAQ 6211 to acquire acceration, strain and temperature from a VI. I have made several modifications and my last two vis are attached. I need to get 1000 data points from a encoder and sampling the period is by far the best way to get acceleration considering my hardware.
Is there a way to ensure that all three variables are synchronised within a timestamp without the vi slowing down?
Sincerely
Ahmad
Attachments:
test_6.vi ‏57 KB
test_5.vi ‏50 KB

The problem lies in synchronising the acceleration with the load and temperature. For acceleration I'm getting a period from a counter with Implicit values (i.e. without specifying timing). I have set the number of samples to acquire to 1000 points and this task does not require sample timing. Post processing the period data in matlab gives me the acceleration.
Now my vi uses a Sample Clock with set number of samples being acquired for the load and temperature. This means that a set number of samples for load and temperature can be acquired and this time may not be enough to acquire the acceleration points; hence they cannot be mapped in time.
The period is implicit and I can't find a way to synchronise with the load and temperature that are acquired at a fixed sample rate. The bottle neck in this problem is to get the acceleration (period recorded) in sync with the load and temperature. If this can be done without any compromise to the speed of the vi then this problem is resolved.
I have attached the vis which will show the development to overcome this problem.
Sincerely
Ahmad
Attachments:
test_1.vi ‏50 KB
test_2.vi ‏49 KB
test_7.vi ‏49 KB

Data acquisition with tktds2xx.llb

Hello,
I use the "TKTDS2XX Read Waveform to Array.vi" from tktds2xx.llb to get data out of my Tektronix TDS 220 over the serial interface. When I made a measurement (trigger modus normal) I always get only the data up to the trigger point and afterwards I have to switch the oscilloscope off/on. Without making a measurement I can read all 2500 points (default setting).
Any suggestions?
Andreas

There is no easy to put a 2D array into a 2D array. We can only replace a subarray into a larger dimension array.
A For loop is the best way to handle it. For loops are very efficeint at handling arrays.
The attached VI (7.1) shows how to process multiple 2D arrays into a larger 2D array. There might be a slightly easier way, but I couldn't think of anything quick.
What it does is breaks the DAQ array down into single elements and then using 'Replace Array Subset', puts them in the initialized array one at time. I added some timing code at teh end to see how fast is runs the "Replacing". Average time on my P4 1.8GHz with 512Ram is 4ms. This was acquiring 1000 samples on 10 channels.
Ed
Ed Dickens - Certified LabVIEW Architect - DISTek Integration, Inc. - NI Certified Alliance Partner
Using the Abort button to stop your VI is like using a tree to stop your car. It works, but there may be consequences.
Attachments:
Replace 2D Array.vi ‏3968 KB

Why ACK should be deasserted sometimes during the data acquisition with PCI-DIO-32HS burst mode handshaking?

My peripheral device sends 32-bit data to the DIO board serially with PCLK 6MHz, about 300,000 times totally. The phenomenan like I mentioned in the summary above happens, and it causes some data missings.
Though I know ACK is not always asserted as somewhere in the NI database says, I want to know why it happens. if I can. I wonder if it is just inevitable or not.
Do I only have to add some buffer memories to my device and make it watch on the ACK changing? Or, is there any other good way to avoid this problem?

Hi,
Burst mode handshaking protocol needs to conditions to be meet before data can be transfered. The PCI-DIO-32HS need to be ready to transfer data and the external device needs to be ready to transfer data.
The ACK line tells the external device when the PCI-DIO-32HS is ready and the REQ line tells the PCI-DIO-32HS when the external device is ready. When both are ready data should be transfered. This is the nature of Handshaking, guarenteed data transfer (when both devices are ready), but not at a guarenteed rate. Handshaking means that the two devices communicate with each other to determine when to transfer data.
The PCI-DIO-32HS ACK line is toggling low because the PCI-DIO-32HS is busy catching up with the given transfer and is not ready to receive m
ore data at this time. The ACK line is not something you can control, it is controlled by the PCI-DIO-32HS.
Your application may be better suited for use with Pattern I/O if you are not using the handshaking lines, ACK and REQ, to control the flow of data. Pattern I/O does not use handshaking lines and clocks data in on every rising edge of the clock. You may receive an error if your system can not keep up with the transfer rate.

HFM DATA LOAD WITH ODI HANGS LONG TIME

Hi all,
     There's a very strange problem when I loading data from MS SQLServer to HFM with ODI. Specifically, there are 2 interfaces to 2 applications on the same HFM server. Data amount is about 1,300,000 and 650,000 separately.
The strange thing is when I execute interface individually, it sometimes works well. However when I execute the package contains 2 interfaces, the larger one almost hangs on about 10+ hours every time whether I use an agent or not.
After some research, it seems that the session hangs on because it cannot get return info from HFM but loading data has already completed. I found some similar problems on OTN like 64bit driver and jre compatible error OR deadlock on table. Different with this one. So, can anyone help on this? Much appreciate in advance!!!
BTW, ODI and HFM are on the same server but ODI repositary and source of interface are on another MS SQL data server. The version is as below:
HFM 11.1.1.3.0.956
ODI 11.1.1.6.0
win server 2003 x86
MS SQLServer 2008 R2
win server 2008 x64
Regards,
Steve

Hi SH,
     source is MS SQLServer 2008 R2, staging area is on the source side, target is a HFM 11.1.1.3.0.956 based on SQLSERVER.
     KM is a standard 'IKM SQL to Hyperion Financial Management Data'.
     No transformation logic but only a filter to select data in current year.
Besides, I have do some performance tuning as guide tolds:
REM #
REM # Java virtual machine
REM #
set ODI_JAVA_HOME=D:\oracle\Java\jdk1.6.0_21
REM #
REM # Other Parameters
REM #
set ODI_INIT_HEAP=512m
set ODI_MAX_HEAP=1024m
set ODI_JMX_PROTOCOL=rmi
In Regedit:
EnableServerLocking: 1
MaxDataCacheSizeinMB :1000
MaxNumDataRecordsInRAM: 2100000
MultiServerMaxSyncDelayForApplicationChanges:300
MultiServerMaxSyncDelayForDataChanges:300
After some reaserch, I think the problem can be located at the HFM-ODI adapter or HFM side(maybe HFM cannot respond a completed info to ODI), do you have any idea? Thanks in advance

"Windows 8 using 100% of HDD with high average response times and low read/write speed"

Turns out this is a fairly well known windows 8.1 issue that has been plaguing users since at least 2013 and there is no one simple fix, so it may not be *entirely* hp's fault; but I've had two of these laptops, both the same model, the first one needing to be returned and exchanged for an entirely unrelated issue (hardware failure: ethernet port nonfunctional with lights stuck on). Both are refurbished. Both have been extreemly slow and unresponsive even compared to a lesser Brazos powered laptop I had before, but I've only recently decided to investigate why.
So if there is something HP specific going on here, I hope there is one simple fix. My average response time has gone up as far as well over a minute (>60,000ms), so I may be an outlier case here compared to the typical windows 8.1 hardrive responsiveness/bandwidth problem.
Edit: there is a case with another HP pavilion laptop (intel powered though, so it may be an intel storage driver issue described in the first link) being much, much worse.
This question was solved.
View Solution.

Guess what just now happened again
So using DISM did _not_ fix it.

Data acquisition with control references

I'm a new LabView user and I would like to acquire data in a subVI and display that data in the main VI. I think that I need to use control references and refnums, but I just haven't been able to figure it out. I would GREATLY appreciate any help I could get.
Thank you!

From your description I would guess that the "subVI" has a loop in it that repeatedly reads the FP hardware, and the indicator is inside the loop. Right?
The thing to do is move a lot of the logic in the subVI up to the Main VI--or add the Main's added logic to the subVI, whichever is easier. In the first case, the subVI would go away, in the second, the subVI would become the Main VI.
If you're confused, post your code in V6.0 format and I'll show you what I mean.
Mike...
Certified Professional Instructor
Certified LabVIEW Architect
LabVIEW Champion
"... after all, He's not a tame lion..."
Be thinking ahead and mark your dance card for NI Week 2015 now: TS 6139 - Object Oriented First Steps

Need help to create file with name and current time stamp.

I need to create .xlsx file exporting data from sql database and file name would be 'FileName' and current yyyymmdd.
I'm trying to use following code but it's keep saying incorrect syntax near "+".
EXEC p_CreateExcel 'sql64', 'NewFile', '\\hrfile1\Shared\Buying Report\NewFile'
+ CAST(YEAR(CURRENT_TIMESTAMP) AS VARCHAR)
+ RIGHT('00'+CAST(MONTH(CURRENT_TIMESTAMP) AS VARCHAR),2)
+ RIGHT('00'+CAST(DAY(CURRENT_TIMESTAMP) AS VARCHAR),2)+'.xlsx'

This is what I have on EXEC p_CreateExcel
USE [XePro01]
GO
/****** Object: StoredProcedure [dbo].[p_CreateExcel] Script Date: 02/26/2015 11:27:35 ******/
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
ALTER procedure [dbo].[p_CreateExcel]
@db_name varchar(100),
@table_name varchar(100),
@file_name varchar(100)
as
--Generate column names as a recordset
declare @columns varchar(8000), @sql varchar(8000), @data_file varchar(100)
select
@columns=coalesce(@columns+',','')+column_name+' as '+column_name
from
information_schema.columns
where
table_name=@table_name
select @columns=''''''+replace(replace(@columns,' as ',''''' as '),',',',''''')
--Create a dummy file to have actual data
select @data_file=substring(@file_name,1,len(@file_name)-charindex('\',reverse(@file_name)))+'\data_file.xls'
--Generate column names in the passed EXCEL file
set @sql='exec master..xp_cmdshell ''bcp "set fmtonly off select * from (select '+@columns+') as t" queryout "'+@file_name+'" -c -t, -T -S'''
exec(@sql)
--Generate data in the dummy file
set @sql='exec master..xp_cmdshell ''bcp "set fmtonly off select * from XeProgst01.dbo.'+@table_name+'" queryout "'+@data_file+'" -c -t, -T -S'''
exec(@sql)
--Copy dummy file to passed EXCEL file
set @sql= 'exec master..xp_cmdshell ''type '+@data_file+' >> '+@file_name+''''
exec(@sql)
--Delete dummy file
set @sql= 'exec master..xp_cmdshell ''del '+@data_file+''''
exec(@sql)
GO

Generic delta has problem with delts pointer time stamp

Hi All,
We have generic delta data source with Delte pointer as Time stamp. We have not used any safety limits. We are loading the data to DSO and using Additive delta. But the problem is when delta flag is set, there might be a case where some records still being inserted to table with lower time stamp. These records are not being fetched in next delta.
We are planning to keep a safety upper limit of 5 min so that those records can not be missed. But we have a doubt as it is a Additive delta duplicate records will be loaded. If we make the delta to 'new status to changed records', it is going to work?? Any other things we have to check when we make this changes??
Thanks
Haaris

Hi
If you had selected additive delta then you can load data to DSo with addition mode only. No overwrite possible.
If you want to select new or changed status then you can load to DSO with overwrite mode only.
Additive or changed delta depends on your requirement because if you want to add data to the DSO then you can go ahead with additive otherwise you have to use DSO with overwrite mode only.
You can either give safety upper limit or lower limit but if you give safety lower limit then you can only load data to DSO with overwrite mode because there could be some duplicate records.
Hope it clarifies.
Regards
Sadeesh

Data acquisition with highly accurate GPS time stamping (hh:mm:ss:sss UT)

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