Missing or invalid +20 kV readback clears the radiation indicator

[bwalkerMIR]

Missing or invalid +20 kV readback clears the radiation indicator

Location: beam_energy.py:606, beam_energy.py:1222

What is wrong: Missing or invalid +20 kV readback clears the radiation indicator.

Exact scenario: +20 kV is above the radiation threshold, then KnobBox/readback communication drops. set_default_values() calls apply_warning_indicators(index, None, None), and _update_radiation_indicator(None) sends False.

Why it matters: Unknown high-voltage state should not extinguish a radiation warning light.

Recommended fix: Treat unknown readback as fail-safe: preserve/assert the indicator, or expose an explicit fault/unknown state instead of sending False.

[chott24]

Analysis on most recent branch - commit c10f225 of PR #180 :

Radiation indicator clears when +20 kV readback becomes missing or invalid

Description

The Beam Energy subsystem currently turns off the Laser Monitor radiation indicator when the +20 kV readback becomes missing or invalid.

The issue is in subsystem/beam_energy/beam_energy.py. _update_radiation_indicator(voltage) coerces missing/invalid readings to None, then computes the radiation indicator state as False unless the readback is a valid numeric value at or above RADIATION_INDICATOR_THRESHOLD_V (10000.0 V).

Several communication-loss paths call set_default_values(index), which sets the display values to -- and calls apply_warning_indicators(index, None, None). For the +20 kV supply, that calls _update_radiation_indicator(None), causing the callback to send False to LaserMonitorDriver.set_radiation_indicator().

Reproduction Scenario

1. +20 kV readback is valid and above the radiation threshold, for example 12000 V.
2. Beam Energy calls the radiation indicator callback with True.
3. KnobBox/readback communication drops, or the +20 kV readback becomes missing/invalid.
4. set_default_values() calls apply_warning_indicators(index, None, None).
5. _update_radiation_indicator(None) sends False.
6. The Laser Monitor driver sends STATE ... radiation=0.

Why This Matters

A missing or invalid readback means the +20 kV state is unknown. It should not extinguish a radiation warning that was asserted from a prior valid high-voltage readback.

This is a safety-signaling false negative: the dashboard can turn off the radiation indicator while the physical high-voltage state may still be hazardous. The code does not appear to disable high voltage; it only changes the warning indicator state. However, because this indicator is safety-related, the behavior should be fail-safe.

Expected Behavior

Missing or invalid +20 kV readback should not clear an asserted radiation indicator.

Recommended policy:

• Valid +20 kV readback >= threshold: assert radiation indicator.
• Valid +20 kV readback < threshold: clear radiation indicator.
• Missing/invalid +20 kV readback: preserve the prior asserted indicator state, or explicitly enter an unknown/fault state.

A minimal safe fix is to latch/preserve the indicator after a valid high readback until a valid below-threshold readback is received.

Suggested Tests

Add unit tests covering:

• 12000 V followed by None does not send False.
• 12000 V followed by invalid/non-finite readback does not send False.
• 12000 V followed by a valid below-threshold value does send False.
• Initial missing readback behavior is explicit and documented.

[chott24]

Functional changes made:

• Beam Energy now remembers the radiation-indicator state from the last valid +20 kV readback in _radiation_indicator_last_valid_state.

• Valid +20 kV readbacks still behave the same:

  • >= 10000 V sends/asserts True to the Laser Monitor radiation indicator.
  • < 10000 V sends/clears False.

• Missing, invalid, or non-finite +20 kV readbacks no longer clear the radiation indicator.

  • If the last valid readback asserted radiation, communication loss preserves that asserted state.
  • If there has never been a valid readback, missing/invalid data sends nothing.

• set_default_values() still resets the Beam Energy display to --, but for the +20 kV supply it no longer indirectly sends False to the Laser Monitor after a prior high-voltage readback.

• Added regression tests covering:

  • Initial missing readback sends no radiation state.
  • High readback followed by None does not send False.
  • High readback followed by invalid/non-finite values does not send False.
  • High readback followed by valid low readback does send False.
  • High readback followed by set_default_values() preserves the asserted indicator.

See commit 30ac935