Brake Monitor
How is the brake monitor safety limit determined, and what is the OSHA/ANSI constraint?
The safety limit is derived from a measured baseline stopping time at the longest expected stopping condition. The monitor is set to allow no more than a 10% increase over the longest measured stopping time, or 10 ms, whichever is longer, for PSDI mode. For other guarding methods, ANSI B11.1 requires that any deterioration invalidating the safety distance calculation must prevent successive strokes.
How does a brake monitor interact with light curtains and presence-sensing devices?
Safety distance for a light curtain is calculated based on machine stopping time. The brake monitor ensures actual stopping time never exceeds the value used in that calculation. If stopping time increases beyond the preset limit, the monitor inhibits the next stroke and may lock out the press until maintenance corrects the problem and a new baseline is established.
What makes a brake monitor control reliable in safety terms?
A control-reliable brake monitor is designed so that a single component failure does not result in loss of the safety function; failures cause a safe state. Typical features include dual channels of timing/position feedback, continuous self-diagnostics, and fail-safe outputs that de-energize to trip. This meets performance levels required by standards like ISO 13849-1 PL d/e.
A brake monitor is a control-reliable sensor and logic system that continuously measures and evaluates the stopping performance of a machine’s braking system, and automatically prevents further operation if stopping time or distance deteriorates beyond a preset safe limit. It is required by OSHA 1910.217 and ANSI B11.1 for mechanical power presses using light curtains, two-hand controls, or barrier guards.
On a shop floor, a brake monitor is installed in the press control circuit and configured with a reference stopping time measured during commissioning. On each stroke, it detects top-of-stroke, measures elapsed time until the slide fully stops, and compares actual stopping performance to a preset safe limit (e.g., no more than 10% increase or 10 ms). If stopping time exceeds the limit, the monitor locks out the next stroke and activates alarms. This ensures that safety distances for light curtains or barriers remain valid. Maintenance uses monitor trends to identify brake wear or hydraulic issues early, integrating data into pre-start checks and periodic performance validation.
Improper or outdated brake monitor settings: Many facilities set the limit once and never re-validate after brake replacement, speed changes, or tooling changes, leading to unsafe safety distances that no longer match actual stopping time.
Defeated or bypassed brake monitor: Operators or maintenance may bypass the monitor's output or ignore warning indicators to keep production running, which is a serious compliance violation and increases risk of hand-in-die incidents.
Lack of documented periodic testing: OSHA and ANSI require documented stopping time measurements and verification that monitor settings reflect actual performance. Common gaps include no test procedure, no recorded stop-time results, and no response to incremental increases in stopping time.