EGT Digital DPG-SD Series Pyrometer + Probe Kit - Marine Engines

Why Marine Installations Require Extended Cable and Specific Hardware

Marine engine installations present a unique constraint: the distance between the engine compartment and the helm. In most inboard and stern-drive configurations, the engine is mounted aft while the operator interface is positioned forward. On larger vessels, that separation can exceed 20–30 feet.

The DPG-SD Marine Kit addresses this by using thermocouple-grade extension wire for the full cable run, rather than relying on short probe leads with field splicing. This ensures the signal integrity of the Type K thermocouple is maintained from the probe tip to the gauge input.

Why Thermocouple Extension Wire Cannot Be Substituted with Copper

A thermocouple circuit generates voltage through the Seebeck effect, which depends on the temperature difference between the measurement junction and the reference junction at the instrument.

Any splice that introduces a dissimilar metal — including copper — creates an additional thermoelectric junction. That junction produces its own temperature-dependent voltage, which adds to the measured signal and introduces error.

In a marine engine compartment, where ambient temperatures can vary significantly, this error is not constant and cannot be calibrated out. Thermocouple extension wire uses the same alloy pair as the probe (Chromel and Alumel for Type K), preventing the formation of unintended junctions and maintaining measurement accuracy.

Probe Selection: Gasoline vs. Diesel Applications

This kit is configured with either an exposed-junction probe for gasoline engines or an enclosed-junction probe for diesel applications.

The diesel configuration uses a Type K thermocouple with an enclosed, ungrounded junction inside an Inconel sheath, designed to withstand sulfur compounds, particulate matter, and condensate commonly found in marine diesel exhaust. 

This enclosed design improves long-term durability, with a response time of approximately 1200 milliseconds (time constant) — appropriate for diesel applications where stability and longevity are more important than rapid transient response. 

Response time is defined as the time required to reach 63.2% of a step temperature change.

Marine-Grade Construction and Corrosion Resistance

The marine kit includes a 316 stainless steel weld bung, selected for compatibility with marine exhaust components exposed to saltwater and condensation. Mild steel bungs are susceptible to corrosion in this environment and are not suitable for long-term marine use.

The probe cable uses 20 AWG stranded conductors with FEP (Teflon) insulation and stainless steel overbraid, providing resistance to heat, oil, fuel vapor, and vibration commonly found in engine compartments. 

Proper installation requires routing the cable away from direct contact with hot exhaust surfaces and securing it to prevent abrasion at bulkheads and panel penetrations.

Probe Construction and Installation

• Thermocouple type: Type K 
• Temperature range: -148°F to 2372°F (-100°C to 1300°C) 
• Accuracy: ±0.4% of reading or ±1.1°C (Special Limits of Error) 
• Probe diameter: 3/16" (0.187") 
• Junction: Enclosed, ungrounded (diesel configuration) 
• Response time: ~1200 ms (time constant) 
• Sheath material: Inconel 
• Cable: 20 AWG, FEP insulated, stainless steel overbraid 

Maximum insertion depth depends on probe hot leg length (for example, approximately 1.1 inches for a 3-inch hot leg), and should be considered when positioning the probe within the exhaust flow. 

Type K polarity must be maintained:

• Yellow = Positive (+) 
• Red = Negative (–)