2.9.1.12 - Line-to-Line Measurement (Mode 14) [U3 Datasheet]

Hello Labjack Support,

I am currently trying to work with the Line to Line Measurement (Mode 14) and having some troubles understanding some of the results. 

Here is a copy of the one of the modified examples I am using in MATLAB:

% ------------------------------------------------------

% Line to Line Period Example: Two timers are set to Mode 14 and are used

% to measure the difference between the two rising edges

% ------------------------------------------------------

clc %clear the MATLAB command window

clear global %Clears MATLAB global variables

ljud_LoadDriver; % Loads LabJack UD Function Library

ljud_Constants; % Loads LabJack UD constant file

Time0 = 0;

Time1 = 0;

[Error ljHandle] = ljud_OpenLabJack(LJ_dtU6,LJ_ctUSB,'1',1); % Returns ljHandle for open LabJack

Error_Message(Error)

% Reset Labjack

Error = ljud_ePut(ljHandle, LJ_ioPIN_CONFIGURATION_RESET, 0, 0, 0);

Error_Message(Error)

% Set the timer/counter pin offset to 0, which will put the first

% timer/counter on FIO0

Error = ljud_AddRequest(ljHandle, LJ_ioPUT_CONFIG, LJ_chTIMER_COUNTER_PIN_OFFSET, 0, 0, 0);

Error_Message(Error)

% 48 MHz Clock

Error = ljud_AddRequest(ljHandle,LJ_ioPUT_CONFIG,LJ_chTIMER_CLOCK_BASE,LJ_tc48MHZ_DIV,0,0);

Error_Message(Error)

% Frequency = 1 MHz

Error = ljud_AddRequest(ljHandle,LJ_ioPUT_CONFIG,LJ_chTIMER_CLOCK_DIVISOR,48,0,0);

Error_Message(Error)

% Enable 2 Timers

Error = ljud_AddRequest(ljHandle,LJ_ioPUT_CONFIG,LJ_chNUMBER_TIMERS_ENABLED,2,0,0);

Error_Message(Error)

% Timer Mode 14: Line to Line Measurement

Error = ljud_AddRequest(ljHandle,LJ_ioPUT_TIMER_MODE,0,14,1,0);

Error_Message(Error)

Error = ljud_AddRequest(ljHandle,LJ_ioPUT_TIMER_MODE,1,14,1,0);

Error_Message(Error)

% Execute above requests

Error = ljud_GoOne(ljHandle);

Error_Message(Error)

% Get all results just to check for errors

Error = ljud_GetFirstResult(ljHandle,0,0,0,0,0);

Error_Message (Error)

% Run while loop until Error 1006 is returned to ensure that the device has

% fully configured its channels before continuing.

while (Error ~= 1006) % 1006 Equates to LJE_NO_MORE_DATA_AVAILABLE

    Error = ljud_GetNextResult(ljHandle,0,0,0,0,0);

    if ((Error ~= 0) && (Error ~= 1006))

        Error_Message (Error)

        break

    end

end   

%Get Timer Reading

%Timer 1 Reading

[Error Time0] = ljud_eGet(ljHandle,LJ_ioGET_TIMER,0,Time0,0); 

Error_Message(Error)

Time0

%Timer 2 Reading

[Error Time1] = ljud_eGet(ljHandle,LJ_ioGET_TIMER,1,Time1,0); 

Error_Message(Error)    

Time1

if Time0 == Time1

    display('Success!') % Display Counter value

    fprintf('Edge Difference is:%fs\n',Time0/1e6);

end

%Reset the timer

Error = ljud_ePut(ljHandle, LJ_ioPUT_TIMER_VALUE, 0,0,0);

Error_Message(Error)

The purpose of that program is just to output the time difference if the timer have matching values (meaning a pulse width has been measured).

I have done tests using two different types of 5V pulse trains, fixed width and variable width, and the results are a bit off compared  to what I have read from your information. <\p>

First tests were done with a 1kHz 5V fixed dely pulse train. At the first device startup, I get:

Time0 = 49993 (the numbers are just for an example)

Time1 = 49993

which is producing a correct result.<\p>

However, when I poll again (nothing about the pulse train has been changed), I get:

Time0 = 0

Time1 = 49993

I understand that Time0 goes to 0 because I reset it and Time1 stays the same because I did not reset it, but shouldn't the Timers measure again and return ~49993 on both Time0 and Time1?<\p>

Now, for tests on a variable pulse train. I turned on the pulse trains and took readings twice, my results were:

Test 1

Time0 = 41810

Time1 = 43076

Test 2

Time0 = 30940

Time1 = 32200

Then, when I unplug the turn off the pulse train, I get the following result:

Time0 = 57630

Time1 = 57630

The numbers match!

So do you have any idea as to why this behaviour is occuring. I had thought based on what I read that the numbers should always match as long as both triggers have been met. I have just started working with this device in MATLAB so I may have set it up wrong. Any help is appreciated.

Many thanks,

Kjell 

So, If understood this feature correctly then Line-to-Line measurement can measures the delta time between an edge on one FIOx line and an edge on another FIOy line by counting the number of clock source ticks between the two FIO edges.

Thanks and Regards, R.