EGT Response Time

Read how to attaining quicker reaction times from EGT thermocouples via DYNO-MAX.

Advanced | 07.28.20

How can I speed up my EGTs response time?

Quicker EGT response time… can be simulated using advanced features in DYNO-MAX “Pro’s” Formula Editor. This example user editable formula, named “Extra Fast EGT #1,” has been included since Version 9.32:

Exhaust Temp #1 + (d/dt ( 0.500 {Exhaust Temp #1} * 0.800 )

Understand that all thermocouple elements take time to register temperature changes. This response lag is referred to as the thermocouple’s “Time Constant,” and represents the seconds to register 63.2% of a temperature change.

Typical heavy-duty (sheathed) probes can take several seconds to reach the exhaust’s actual temperature. Even exposed junction probes – using very fine (and fragile) wire – still have Time Constants measured in tenths of a second. In other words, thermocouples suitable for daily dynamometer testing fall far short of providing instantaneous response.

Fortunately, there is a way to compensate for this latency. When the medium- in this case exhaust gases – and their average velocity are relatively consistent, it becomes practical to extrapolate the true exhaust temperature from a thermocouple’s rate of change.

DYNO-MAX’s “Derivative” formula feature can easily resolve this Delta Temperature and then multiply it by a scaling constant* – returning the current temperature lag deviation. We add this correction value to the normal EGT reading – for a close estimate of the true instantaneous temperature.

*The “scaling constant” can be experimentally determined by recording EGT readings – while rapidly opening, holding, and then rapidly closing the throttle (under load). Graph and compare both the standard EGT #1 and the Extra Fast EGT #1formulas. Then edit the Extra Fast EGT #1 formula’s scaling constant (default is 0.800) until the Extra Fast EGT #1 response is close to instantaneous (without overshooting the steady state EGT #1 temps).

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