Protect High Value Tests

Independent Thermal Fail-Safe (IFS)

TotalTemp’s Independent Thermal Fail-Safe Systems provide a truly independent layer of protection for any thermal test environment. These systems operate outside the primary temperature controller and are designed to shut down
heating, cooling, or DUT power when preset temperature limits are exceeded. The result is a reliable, redundant safeguard against thermal runaway, unintended cooling, loss of cooling capacity, or active load overheating.

These units can be retrofitted to most existing Thermal Platforms, Temperature Chambers, Hybrid Chambers, or custom
thermal systems. Each system is configurable for high limit or low limit protection and supports thermocouple or RTD. Audible alarms, visual indicators, and optional digital notifications (via Synergy Nano) provide clear operator awareness during both attended and unattended testing.

Rackmount and benchtop configurations are available, covering temperature ranges from –200°C to +1260°C, suitable for ESS, space simulation, cryogenic testing, and high temperature materials evaluation.

Redundant Fail-Safe

The red circle indicates the PM3 high / low limit temperature controller. A redundant fail-safe with a PM3 Limit Controller
works differently than the IFS. It uses an independent RTD sensor to monitor temperature and actuates a redundant
cryogenic cutoff valve to physically stop LN₂ flow. In addition to closing the valve, the PM3 also cuts power to the
main power relay, removing power from heaters and blowers while keeping the controller itself energized. Together,
the valve and relay shutdown ensure the chamber or platform cannot continue cooling or heating during a fault.

In summary, the IFS provides an external, controller independent electrical safety layer, while the PM3 redundant
valve system provides an internal, cryogenic specific mechanical and electrical shutdown. Using both creates a
layered, highly robust safety architecture.

How the Fail-Safe Protects the Device Under Test (DUT)

1. Independent sensor monitors the DUT or chamber temperature and detects when the safe limit is exceeded.
2. The Fail-Safe immediately removes power from heaters, cooling, or the DUT itself, stopping further heat generation
   or runaway conditions. For cryogenic systems, full protection requires a redundant LN₂ valve, since removing power
   alone cannot stop cooling if a primary valve sticks open. The system latches in a safe state, preventing automatic
   restart until manually reset.
3. Audible and visual alarms alert operators; with Synergy Nano integration, digital notifications can be sent to remote users during unattended cycling.
4. Why it matters: Prevents catastrophic overheating, PCB delamination, component popcorning, lithium-based thermal
   events, unintended deep cold exposure, or structural damage to aerospace hardware.

Thermal Testing Limit Safety Overview

Temperature chambers and thermal platforms inherently carry risks when operating at extreme temperatures. Protecting both the test article and the equipment requires multiple layers of safety:

1. Controller level limits: Prevent users from requesting unsafe temperatures.
2. User set limits: Protect sensitive DUTs from accidental over temperature conditions.
3. Alarm shutdown modes: Triggered when the primary sensor reads outside the allowed range.
4. Independent limit controllers (fail-safes): Provide protection when control hardware fails, relays stick, or human error occurs.
5. Redundant LN₂ valves: Strongly recommended for cryogenic systems where removing power alone cannot stop cooling.
6. Active load shutdown: Ensures DUTs or high velocity blowers cannot continue generating heat after a fault.

Cryogenic Valve Care

Valve cycle counter for maintenance monitoring.
Cryogenic or refrigeration valve cycle counters track the number of actuations for maintenance planning. Solenoid valves rely on a plunger mechanism with an expected service life of roughly ten million cycles, so monitoring cycle count helps ensure the valve is serviced before wear prevents reliable actuation.

Debris, Valve Failures, and the Importance of Cryogenic Filters

Cryogenic systems depend on reliable flow through valves, orifices, and small passages. Over time, debris such as rust,
scale, Teflon tape fragments, elastomer particles, and general contamination can accumulate in the plumbing. Without
proper filtration, this debris is carried directly into cryogenic valves where it can interfere with sealing surfaces
and moving parts.

When debris reaches a cryogenic valve, several failure modes are possible:

• Valve stuck open: Particles prevent the valve from fully closing, causing continuous flow and potential runaway cooling.
• Valve stuck closed or restricted: Debris blocks the seat or orifice, starving the system of coolant and causing loss of cooling capacity.
• Erratic operation: Contamination causes intermittent sticking, chatter, or unstable flow, making control unreliable and difficult to diagnose.

A properly selected cryogenic filter installed upstream of critical valves captures this debris before it can cause
mechanical or sealing problems. This improves valve reliability and enhances the predictability and repeatability of
thermal performance, especially in unattended or long-duration tests.

Freezing the Plunger

If a delivery hose is removed and reattached while below the dew point, moisture can condense and freeze inside the hose. This ice can foul the valve plunger and prevent it from closing. In rare cases, the plunger can freeze to the
guide, causing a stuck-open condition where coolant continues flowing even with power removed.

The solution is simple: always blow out the delivery hose before attaching it to the cooling valve. This clears any moisture that may have formed on the cold inner walls of the hose. Do not point the hose toward yourself or others a slight crack of the valve (¼ turn) for a brief moment is sufficient before shutting it off and connecting the hose.

Thermal systems fail in predictable ways

The best protection comes from addressing those failure modes directly. Independent limit control, redundant valve shutdown, and proper cryogenic maintenance form a complete safety strategy that works in real labs, not just on paper. TotalTemp builds safety systems that work the way test labs actually operate, giving you protection you can trust, performance you can depend on and protect high value tests.

Planning Ahead

It is always best to plan ahead when specifying new thermal test equipment. Existing chambers that lack sufficient built-in protection can often be upgraded with integrated limit controllers that use independent sensing and internal system shutdown capabilities. When internal retrofits are not practical, an external fail-safe controller can provide the required level of protection. TotalTemp Technologies offers a full range of safety controls for thermal platforms, hot/cold plates, TVAC systems, and all standard temperature chambers.