3618 Engine Caterpillar

Metal Particle Detectors

Illustration 1	g00866217
Front view and left side view of the metal particle detectors

The engine has two metal particle detectors. The detectors are electrical sensors that detect the presence of metal particles in the engine oil.

Metal particles from worn components such as bearings, piston rings, and gears can be suspended in the engine oil. Detection of the particles will activate an alarm or a shutdown in order to alert the operator of the condition. Corrective maintenance that may prevent more costly repairs can then be performed. For example, replacement of a main bearing may prevent the need to replace a crankshaft.

Illustration 2	g00866265
Schematic of the electrical grids (A) Open circuit (B) Closed circuit

The two metal particle detectors are parallel in the flow of engine oil. Engine oil is continuously circulated through the detectors. Each detector contains a perforated board with tin plated electrical grids. The grids are an open circuit. The engine oil flows between the grids. If a metal particle closes the gap between the grids, the circuit is closed.

Each detector has an input to the programmable logic controller. If either one of the detectors senses metal particles, an alarm is generated. If both of the detectors sense metal particles, a shutdown is generated.

Oil Mist Detector

Illustration 3	g00866329
Oil mist detector

The oil mist detector helps protect the engine against serious damage that can originate from the overheating of bearings and/or piston components.

The oil mist detector uses a vacuum and individual pipes that draw the atmosphere from each compartment. If the oil mist exceeds the threshold, the alarm relay is activated. The detector then determines the source of the oil mist. Valves for all of the pipes are sequentially opened and closed in order to sample the atmosphere from each compartment. Groups of compartments are compared. The compartment with the alarm is indicated on the face of the detector.

For detailed information on the detector, refer to Service Manual, RENR2225, "Oil Mist Detectors".

Resistance Temperature Detectors (RTD)

Illustration 4	g00878169
Resistance temperature detector (1) Connector (2) Thermowell (3) Element

An RTD is a sensor that is used to measure temperature. The electrical resistance of the sensor is a function of temperature.

Thermowell (2) is inserted into a liquid or gaseous fluid. A known current is supplied to element (3). The voltage drop across the element is measured. The temperature of the element has a linear effect on the element's resistance. As the temperature increases, the resistance and the voltage drop increase. As the temperature decreases, the resistance and the voltage drop decrease. The voltage drop is interpreted as a temperature.

Illustration 5	g00878185
Electrical schematic of an RTD (1) Return terminal (2) Supply terminal (3) Sense terminal

In addition to the current supply and return wires, a third wire is used. The resistance of a sensor with two wires can be calculated but the three wires enable the monitoring system to calculate the element's resistance with more accuracy. The element's resistance is calculated from the equation in Table 1.

Readings from an RTD are used for display on the control panel and for activation of alarms by the monitoring system.

The parameters that are monitored for temperature with an RTD are listed in Table 2.