FLO-TECH SPEED CONTROL ELECTRONIC SPEED CON Caterpillar


Chapter 4 Description of Operation

Usage:

Introduction

The Woodward Flo-TechTM Speed Control provides precise speed control of an engine with separate dynamics for stable, responsive engine operation at rated and idle speeds.

Electronic Circuits

All circuits in the Flo-Tech Speed Control are solid state and are not serviceable in the field. The printed circuit board is manufactured by Woodward to provide maximum tolerance to temperature and vibration. Components are wave soldered to the board, and the circuits are computer-tested to assure maximum dependability and accuracy.

Potentiometers, accessible through the control-box case or input through the terminal board, provide all adjustments to the control system. A 10-turn potentiometer provides precise adjustment of the rated-speed setting. One-turn potentiometers provide adjustment for rated speed, fuel limit, idle or unloaded gain and stability, and rated or loaded gain and stability. In addition, the control can be fitted with external potentiometers to set the idle speed and to trim the rated speed from a remote location.

Speed Control

The control converts the signal from the magnetic pickup on the engine into a dc voltage level which is proportional to engine speed. This voltage level is compared to the rated or idle speed setting. After the speed error is modified by GAIN, STABILITY, and SPEED TRIM, the result is sent to a driver that provides 0-200 mA to the Flo-Tech Throttle installed on the engine.

Stability and Gain

The stability and gain adjustments on the Flo-Tech Speed Control allow tailoring of the response rates at idle and at rated speeds to match the engine being controlled.

STABILITY adjustments affect engine reaction time when recovering after a sudden load change. The magnitude of the speed change resulting from a sudden change in load is controlled by the GAIN adjustments.

Start Fuel Limit

A one-turn pot is available to set a start-fuel limit. The Start Fuel Limit provides a maximum fuel flow until the engine is at idle or rated speed, as selected. When the fuel-limit potentiometer is set fully counterclockwise, the valve will go to a low-fuel position until selected speed is reached. Fuel limiting can prevent smoke during startup, can aid starting on some types of engines, or can be used to prevent excessive overspeed as an engine reaches rated or idle speed. Fuel limit is automatically enabled when the MPU signal falls to zero, and disabled just before the engine reaches idle or rated speed.

Failed Speed Sensor

A safety circuit is included in the Flo-Tech Speed Control to cause the throttle to go to minimum position if the signal from the magnetic pickup is lost. This is protection against loss of control should either the magnetic pickup instrument or the wiring from the magnetic pickup to the control fail. Without this safety circuit, the valve would go to maximum or to the fuel limit should the control lose the magnetic pickup signal.

Auxiliary Input

The auxiliary input is provided to allow the Flo-Tech Speed Control to be used with a load sensor or other auxiliary device such as a process control or SPM-A. A Load Sensor is used with the control for isochronous or electrical droop paralleling. With an isolated bus, isochronous load sharing is usually selected. In isochronous operation, the Load Sensor produces a load signal which is shared with the other Load Sensors on line through the parallel lines. The parallel-line voltage represents the average load of the units on line. By comparing the paralleling-line voltage to its own load, the load sensor calculates an output applied to the auxiliary input of the Flo-Tech control. This output raises or lowers, as necessary, the generator output to make the load of its unit equal to the average load. The load-sensor output directly biases the speed-loop circuit of the speed control to affect the fuel-level setting and precisely maintain its proportional share of system load while maintaining a fixed frequency.

Ramp Generator

A Ramp Generator may be attached to terminals 10 (+) and 2 (-) to slow the speed change between idle and rated speeds. Once set, it provides a constant speed change per second by biasing the speed reference when changing from idle to rated and vice versa. Accel and Decel pots on the ramp generator control the rate of change.

A capacitor can be connected between terminals 10 and 2 to provide a non-linear ramp between idle and rated and between rated and idle. This method provides the same rate for both acceleration and deceleration, about one second of ramp time per 50 ?F of capacitance (200 ?F maximum). The capacitor must be 15 Vdc minimum working voltage with less than 30 ?A dc leakage over the operating temperature range.

Speed Trim

A potentiometer can be installed to terminals 9 (counterclockwise) and 10 (clockwise and wiper) to provide remote trim of rated speed. A 1 kOhms potentiometer will provide ±2.5 percent change of rated speed. A 2 kOhms potentiometer will provide ±5 percent change in rated speed. The control is not subject to temperature drift, and the potentiometer for remote speed trim is not usually needed in a single-engine application.

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