Use Case: Multi Sensor Shared Threshold

Use Case: Multi-Sensor Shared Threshold

Plot multiple sensors on a single tile with one shared threshold, see violation markers for all sensors, and run event detection.

When to use: You have several sensors that share the same physical limit (e.g., max temperature across zones, pressure across channels) and want a single threshold line with violations and events computed for each sensor.

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Quick Example

setup;

%% Create sensors with identical threshold rules
sensors = cell(1, 4);
names = {'Zone A', 'Zone B', 'Zone C', 'Zone D'};
x = linspace(0, 60, 500000);

for i = 1:4
    s = Sensor(sprintf('zone_%d', i), 'Name', names{i});
    s.X = x;
    s.Y = sin(x * 2 * pi * i / 20) + 0.3 * randn(1, numel(x)) + 3;

    % Same threshold rule for every sensor
    s.addThresholdRule(ThresholdRule(4.5, 'Direction', 'upper', 'Label', 'Max Temp'));
    s.resolve();

    sensors{i} = s;
end

%% Plot all sensors on a single tile
fp = FastPlot();
for i = 1:numel(sensors)
    % Show threshold line only for the first sensor to avoid duplicates
    fp.addSensor(sensors{i}, 'ShowThresholds', (i == 1));
end
fp.render();
title(fp.hAxes, 'Multi-Sensor — Shared Threshold');
legend(fp.hAxes, 'show');

%% Detect events for all sensors
detector = EventDetector('MinDuration', 0.5);
allEvents = [];
for i = 1:numel(sensors)
    evts = detectEventsFromSensor(sensors{i}, detector);
    if ~isempty(evts)
        allEvents = [allEvents, evts];
    end
end
fprintf('Detected %d events across %d sensors.\n', numel(allEvents), numel(sensors));

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How It Works

1. Threshold on the Sensor, not just the plot

Each Sensor gets the same ThresholdRule. When you call resolve(), each sensor independently computes:

• ResolvedThresholds — the threshold step-function line
• ResolvedViolations — the (X, Y) points that exceed the limit

This means every sensor carries its own violation data, which is required for event detection.

2. Avoid duplicate threshold lines

When calling addSensor(), pass 'ShowThresholds', true only for the first sensor. All subsequent sensors use 'ShowThresholds', false. This draws the threshold line once while still computing violations for every sensor.

Alternatively, skip ShowThresholds entirely and add the threshold manually:

for i = 1:numel(sensors)
    fp.addSensor(sensors{i}, 'ShowThresholds', false);
end
fp.addThreshold(4.5, 'Direction', 'upper', 'ShowViolations', true, ...
    'Label', 'Max Temp', 'Color', 'r');

This approach draws a single shared threshold line and FastPlot computes violation markers against all lines on the tile during rendering (see updateViolations in FastPlot.m).

3. Event detection works per-sensor

detectEventsFromSensor() reads each sensor's ResolvedViolations and groups consecutive violation points into Event objects. Since each sensor resolved independently, events are attributed to the correct sensor:

% Each event knows which sensor it came from
for i = 1:numel(allEvents)
    fprintf('  %s: %.1fs – %.1fs (peak %.2f)\n', ...
        allEvents(i).SensorName, ...
        allEvents(i).StartTime, allEvents(i).EndTime, ...
        allEvents(i).PeakValue);
end

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With State-Dependent Thresholds

The shared threshold can also be state-dependent. Attach the same StateChannel and conditional ThresholdRule to each sensor:

for i = 1:numel(sensors)
    sc = StateChannel('mode');
    sc.setData(modeX, modeValues);   % same state for all
    sensors{i}.addStateChannel(sc);

    % Threshold only active during 'run' mode
    sensors{i}.addThresholdRule(ThresholdRule(4.5, ...
        'Direction', 'upper', 'Label', 'Run HI', ...
        'Condition', struct('mode', 'run')));
    sensors{i}.resolve();
end

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With EventViewer

Display all events in the Gantt-style EventViewer:

viewer = EventViewer(allEvents);

Each event row shows the sensor name, threshold label, and time span. Click any event to drill down into the data.

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Key Points

Aspect	Behavior
Threshold line	Drawn once (first sensor or manual addThreshold)
Violation markers	Computed for every line on the tile
Event detection	Per-sensor via detectEventsFromSensor() — requires resolve() on each sensor
State-dependent thresholds	Supported — attach identical StateChannel + ThresholdRule to each sensor
EventViewer	Shows events from all sensors, attributed by name

See Also

• Sensors — Sensor, ThresholdRule, StateChannel
• Event Detection — EventDetector, detectEventsFromSensor, EventViewer
• Examples — example_multi, example_sensor_dashboard, example_event_detection_live