How to prescribe an analog output when condition is met in analog input using background data acquisition?
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I'm following the example about how to acquire continuous and background data using NI devices (see code below). As in the example, I would like to detect a unique event in the analog input data (e.g., when voltage is greater than 1 V). However, instead of stopping the acquisition when the condition is met, I would like to continue data acquisiton and prescribe an analog output voltage (say, using NI 9263 on cDAQ1Mod2). If the condition is no longer met, I would like to set the analog output voltage to zero. How would I go about achieving this?
Thank you!
%% Acquire Continuous and Background Data Using NI Devices
%
% This example shows how to acquire analog input data using non-blocking
% commands. This allows you to continue working in the MATLAB command window
% during the acquisition. This is called *background acquisition*.
% Use *foreground acquisition* to cause MATLAB to wait for the
% entire acquisition to complete before you can execute your next command.
%
% Copyright 2010-2019 The MathWorks, Inc.
%% Create and Configure the DataAcquisition Object
% Use |daq| to create a DataAcquisition object and |addinput| to add an
% input channel to it. This example uses an NI
% 9205 module in National Instruments(R) CompactDAQ Chassis NI cDAQ-9178.
% This is module 1 in the chassis.
dq = daq("ni");
addinput(dq, "cDAQ1Mod1", "ai0", "Voltage");
dq.Rate = 2000;
%% Plot Live Data as It Is Acquired
% During a background acquisition, the DataAcquisition can handle acquired
% data in a specified way using the |ScansAvailableFcn| property.
dq.ScansAvailableFcn = @(src,evt) plotDataAvailable(src, evt);
%% Set ScansAvailableFcnCount
% By default, the ScansAvailableFcn is called 10 times per second. Modify
% the |ScansAvailableFcnCount| property to decrease the call frequency.
% The ScansAvailableFcn will be called when the number of points
% accumulated exceeds this value. Set the ScansAvailableFcnCount to the
% rate, which results in one call to ScansAvailableFcn per second.
dq.ScansAvailableFcnCount = 2000;
%% Start the Background Acquisition
% Use |start| to start the background acquisition.
start(dq, "Duration", seconds(5))
%%
% There are no other calculations to perform and the acquisition is set to
% run for the entire five seconds. Use |pause| in a loop to monitor the
% number of scans acquired for the duration of the acquisition.
while dq.Running
pause(0.5)
fprintf("While loop: Scans acquired = %d\n", dq.NumScansAcquired)
end
fprintf("Acquisition stopped with %d scans acquired\n", dq.NumScansAcquired);
%% Capture a Unique Event in Incoming Data
% Acquire continuously until a specific condition is met. In this example,
% acquire until the signal equals or exceeds 1 V.
%%
dq.ScansAvailableFcn = @(src,evt) stopWhenEqualsOrExceedsOneV(src, evt);
%%
% Configure the DataAcquisition to acquire continuously. The listener detects the
% 1V event and calls |stop|.
start(dq, "continuous");
%%
% Use |pause| in a loop to monitor the number of scans acquired for the
% duration of the acquisition. Note that the status string displayed by the
% |ScansAvailableFcn| may appear before the last status string displayed by
% the while loop.
while dq.Running
pause(0.5)
fprintf("While loop: Scans acquired = %d\n", dq.NumScansAcquired)
end
fprintf("Acquisition has terminated with %d scans acquired\n", dq.NumScansAcquired);
dq.ScansAvailableFcn = [];
%%
function plotDataAvailable(src, ~)
[data, timestamps, ~] = read(src, src.ScansAvailableFcnCount, "OutputFormat", "Matrix");
plot(timestamps, data);
end
function stopWhenEqualsOrExceedsOneV(src, ~)
[data, timestamps, ~] = read(src, src.ScansAvailableFcnCount, "OutputFormat", "Matrix");
if any(data >= 1.0)
disp('Detected voltage exceeds 1V: stopping acquisition')
% stop continuous acquisitions explicitly
src.stop()
plot(timestamps, data)
else
disp('Continuing to acquire data')
end
end
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Respuestas (1)
arushi
el 29 de Jul. de 2024 a las 9:23
Hi Lesley,
I understand from your query that you want to continue the data acquisition and prescribe an output voltage based on a condition.
To achieve this, firstly add an analog output channel. You can do this using the ‘addoutput’ function.
addoutput(dq, "cDAQ1Mod2", "ao0", "Voltage");
You can learn more about it from the following documentation:
Next, you need to modify the ‘stopWhenEqualOrExceedsOneV’ function as below:
function stopWhenEqualsOrExceedsOneV(src, ~)
[data, timestamps, ~] = read(src, src.ScansAvailableFcnCount, "OutputFormat", "Matrix");
if any(data >= 1.0)
disp('Detected voltage exceeds 1V: setting analog output voltage')
outputVoltage = voltageValueIfConditionIsMet; % Set to a desired voltage level
outputSingleScan(src, outputVoltage); % Set analog output voltage
plot(timestamps, data)
else
disp('Voltage is below 1V: setting analog output voltage to zero')
outputSingleScan(src, 0); % Set analog output voltage to zero
disp('Continuing to acquire data')
end
end
Instead of stopping the acquisition explicitly using ‘src.stop()’, set the output voltage to a value based on the condition. You can use ‘outputSingleScan’ to write your data to the output channel. You can learn more about it here:
Hope it helps.
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