Load test a fixture

Some faults only exist while a fixture is working: a dimmer module that draws no current, a fan that never speeds up, an over-temperature that needs the unit lit for a while. A load test finds them. It lights the fixture, reads its sensors while it is lit, ends output, and says which sensors moved and what appeared that was not there at rest.

The fixture goes bright and hot while it runs. Point it somewhere safe, keep hands clear of moving parts, and never run it on a fixture that is patched into a running show.

Run it from the Monitor tab, from the command line, or by asking an AI assistant connected to the bench (see below).

In the app

Select the fixture and choose Fixture → Load Test… (⇧⌘L) (macOS). The app opens the Monitor tab, starts monitoring the fixture if it is not already being watched, and asks before anything is lit. While a session is running, Put Under Load… on the Monitor tab does the same.

The sheet shows the safety warning, then:

• Level: what every channel is held at, 255 by default.
• Hold for: from 30 seconds to 10 minutes. A temperature needs minutes; a fan shows in seconds.
• Channels at their own level: channels where full is not output, written as 9=0, 10=0. These win over everything else.
• What goes up: the channels the fixture’s own layout or the model’s profile holds lower, in the bench’s words, before you commit.

While the fixture is lit, a bar across the Monitor tab counts down to the end and reminds you to watch the unit. The stretch under load is shaded on the chart, so a climb that starts with it and a cool-down after it are easy to read. End Load brings output down early. Either way the monitor keeps running, so the cool-down is recorded too.

When output ends, the bar says what the load found. Before and After… opens each sensor’s reading before and after the load. The same section is in the session’s summary when you stop monitoring, and it is saved with the session. Each run is also saved under the unit, and the repair sheet lists every run of the repair. Stopping the monitor while the fixture is lit ends output first.

A load test cannot start while you are holding levels with Send DMX: release them first. While a fixture is under load, Send DMX and Walk Channels are unavailable. The whole-line monitor has no load test: a line is not loaded one unit at a time.

What it does

1. Reads every sensor at rest, as the starting point. In the app, that is the monitor’s latest reading of each, taken just before output goes up.
2. Holds every channel of the fixture’s footprint at full, 255, for two minutes unless told otherwise. On a dimmer rack, every module’s channels are driven.
3. Reads the sensors again every second while the fixture is lit, noting any status message that appears.
4. Ends output, then reports each sensor’s reading before and after.

Output is always ended before the test finishes: when it completes, when it is stopped early, and when the fixture stops answering. If the bench cannot end it, the report says so in as many words, and the fix is to unplug the widget or power the fixture down.

A fixture that reports no sensors is refused rather than driven, because there would be nothing to read back.

Channels where full is not output

Full on every channel does not always mean fully lit. On many fixtures a channel selects a color macro, a program or a dimmer mode, and 255 there picks something else. An ADJ 5PX held at full on every channel lit UV only, because its channel 9 at 255 is a color macro.

• When the fixture reports its channel layout (SLOT_INFO), the channels it calls a macro, a color wheel, an effect, a speed or a control are held at the fixture’s own default — or 0 where it gives none — and the report lists them. The rest go to the level.
• When the bench has a profile for the model that says which channels to hold lower in the personality the fixture is in, those channels are set for you, over the fixture’s own layout, and the report names the profile it used.
• Otherwise every channel goes to the same level. When the fixture does not report its channel layout either, the report says the footprint was driven without knowing which channel does what.

A channel you name yourself with --slot wins over both.

Watch the fixture while it runs. The bench cannot see color or where the fixture points; only you can. If it did not look fully lit, hold the macro, program or mode channels at their own level (see --slot below) and run it again.

Reading the result

The first line says how many sensors moved, and whether a condition appeared that was not there at rest. Then each sensor, before and after, those that moved first.

• A current or load sensor that does not move while its neighbors do is a blown lamp, a dead dimmer or an output that is not switching. It is the reading you would otherwise take with a meter.
• A fan still at its idle speed under full output is a fan-control fault. That shows in seconds.
• A temperature needs minutes. Run a longer hold when the question is whether the fixture overheats.
• Appeared under output lists the status messages that came up while the fixture was lit: the over-current or over-temperature it never shows at rest. When there is one, it is usually the answer.
• Nothing moved is inconclusive, not a pass. A sensor slower than the hold, a personality that ignores these channels and a healthy fixture all read the same way.

What moved is not proof of why it moved. A fixture still warm from the last time it ran reads the same way. A sensor that rises each time the level goes up, over more than one run, is the finding to trust.

Short frames

The bench sends a DMX frame that ends at the fixture’s last channel, not all 512, because some fixtures miss RDM requests while a long frame is on the line. The report says where the frame ended. A fixture patched past that point sees no signal.

From the command line

rdmbench-cli load tests the first fixture found, or the one whose UID you give it, and prints each change as it happens and the result at the end. Press Ctrl-C to end it early: output is brought down first.

• --seconds sets how long to hold, 120 by default.
• --level sets the level for every channel, 255 by default.
• --slot CHANNEL=VALUE holds one channel at its own level, counted from the fixture’s start address. Repeat it for more channels. On the ADJ 5PX in 12-channel mode, --slot 9=0 --slot 10=0 --slot 12=0 lights it fully.
• --full-frame sends all 512 channels instead.
• --json prints the result as JSON.

Asking an assistant

An AI assistant connected to the bench can run the same test: ask it to load test the fixture. It is told the fixture goes bright and hot, to check with you before driving a unit you have not just asked about, and that it cannot see color or position, so it will ask you to watch the fixture while the test runs. A test can last up to ten minutes.