EGT, CHT, IAT, TIT, OAT Probe – 2.0 oz
This probe exemplifies true quality engineering. J.P. Instruments fast-response temperature probes deliver industry-leading speed and accuracy, verified through independent scientific testing.
The data shown is based on a controlled study conducted by General Aviation Modifications Inc. (GAMI) on July 2, 2001, using a six-cylinder IO-540 engine. Brand-new probes were installed on each cylinder, positioned 3 inches from the exhaust flange. The test compared grounded and ungrounded thermocouple designs.
The results clearly demonstrate that ungrounded (insulated) probes respond significantly slower to temperature changes and never reach true temperature values. In contrast, JPI’s grounded probes track real-time temperature changes accurately. The ungrounded probes tested were 3/16" in diameter, while JPI’s grounded probes measured just 1/16". At exhaust temperatures approaching 1600°F, larger probes lose heat rapidly due to increased surface area, radiating energy at a rate proportional to temperature to the fourth power. This is why JPI designs thin, fast-response probes rather than bulky, sluggish ones.
Thermocouple response time is defined as the time required for a temperature change to be detected and displayed. According to Thermo Electric Co., typical response times using a 1/4" sheath are approximately 4.5 seconds for ungrounded probes and 1.7 seconds for grounded probes. Fast response is especially critical during engine leaning—only a quick probe can accurately identify peak temperature. Slow probes may indicate peak too late or not at all, increasing the risk of operating excessively lean, which can lead to detonation and engine damage.
JPI probes accurately capture the small, rapid temperature changes that occur during mixture adjustment. Slower, ungrounded probes tend to average these changes and miss critical data entirely.
Accuracy should not be confused with display resolution. While some instruments display temperatures in one-degree increments, that does not guarantee one-degree accuracy. JPI instruments are both displayed in one-degree increments and certified accurate to ±1°F (TSO approved). Many competing systems are only accurate to ±10°F despite similar displays.
To extend probe life, some manufacturers increase probe mass or diameter, but this compromises accuracy and responsiveness. As shown in the test results, larger ungrounded probes never reach true temperature. This can result in unknowingly exceeding turbine temperature limits. JPI’s grounded probes are manufactured from Hastelloy-X, a high-performance alloy designed to withstand the harsh sulfur environment of high-temperature exhaust gases. These probes are used across JPI’s entire product line, including the legendary EDM-700.
If accuracy and response time matter, J.P. Instruments sets the standard.
Reference: “Temperature Measurement Designer’s Guide,” Thermo Electric Co., page K-88.
