EGT Digital DPG-SD Pyrometer Gauge + Probe Kit - Diesel Race Series DF

The APG-SD analog pyrometer gauge and EGT-DF probe combination shown on this page has been discontinued and is no longer available for purchase. For current diesel EGT monitoring, the DPG-XR Diesel Race Kit is the direct production replacement. It uses the same EGT-DF enclosed-tip probe series with a modern digital display, programmable alarm relay, and dual-channel capability. 

The information below is preserved as a technical reference for existing APG-SD installations.

Why the Scale Ran to 600°C Instead of 900°C

A common point of confusion for users familiar with gasoline EGT systems is the lower temperature range of the diesel-specific gauge. Most gasoline pyrometers display up to 1600°F (871°C) or higher, while the APG-SD gauge displayed to 600°C (1112°F).

This difference reflects the physics of diesel combustion. Diesel engines operate with excess air — typically in the range of 20:1 to 80:1 air-fuel ratio, compared to gasoline engines operating near stoichiometric conditions. The excess air dilutes the combustion gases, resulting in lower exhaust temperatures.

Typical diesel exhaust temperatures at the manifold fall in the 400–700°C range, and a higher-range gasoline gauge compresses this operating window into a smaller portion of the dial. By scaling the gauge to 100–600°C, the APG-SD spreads the usable diesel temperature range across the full face, improving visual resolution and making meaningful changes easier to interpret.

Gauge Movement and Display Behavior

The APG-SD used a stepper motor-driven analog pointer rather than a traditional D’Arsonval movement. Instead of relying on coil current for continuous deflection, the stepper motor positions the needle in discrete steps based on the thermocouple input signal.

This produces a digitally controlled pointer that maintains accuracy across the operating range. At very slow temperature changes, individual step increments may be visible, but this has no effect on measurement accuracy.

The gauge also included a white LED backlit dial and a red LED alarm indicator that illuminated when the measured temperature exceeded the programmed setpoint.

EGT-DF Probe Design for Diesel Exhaust

The EGT-DF probe uses a Type K thermocouple with an enclosed, ungrounded junction inside an Inconel sheath, specifically designed for diesel exhaust environments. 

Diesel exhaust contains sulfur compounds that can form corrosive acids in condensate, which can degrade exposed thermocouple junctions over time. The enclosed tip protects the sensing element from direct exposure, significantly improving longevity and stability.

The probe has a response time of approximately 550 milliseconds (time constant), which is appropriate for diesel applications where durability and measurement stability are prioritized over ultra-fast transient response. 

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

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: 1/8" (0.125") 
• Junction: Enclosed, ungrounded 
• Response time: 550 ms (time constant) 
• Max insertion depth: 1.35 inches 
• Sheath material: Inconel 
• Cable: 20 AWG stranded, Teflon insulated, stainless steel overbraid 

The probe includes a 316 stainless steel adjustable compression fitting with 1/8"-27 NPT threads for installation in a standard exhaust port. 

Type K polarity must be maintained:

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