Sensors provide the VIMS modules with input information about changing conditions. The sensors provide information such as speed and temperature. The sensor signal changes in a proportional manner in order to reflect the changing condition. The types of sensor signals that are recognized by the VIMS modules are listed here:
Frequency - The sensor produces an AC signal that varies in frequency (Hz) as the condition changes.
Pulse width modulated (PWM) - The sensor produces a digital signal with a duty cycle that varies as the condition changes. The frequency of this signal is relatively constant and the frequency contains no information.
Frequency Sensors
Frequency sensors produce a sine wave signal or square wave signal that varies in frequency (Hz) as the condition changes.
Suspension Cylinder Pressure Sensor
 | |
| Illustration 1 | g00482617 |
Suspension Cylinder Pressure Sensor (1) Schematic symbol (2) Sensor | |
Suspension cylinder pressure sensor (2) reacts to the pressure in a suspension cylinder. The sensor receives operating power from the machine electrical system. The sensor sends a square wave signal that increases in frequency as the suspension cylinder pressure increase to the VIMS interface module. The signal voltage is relatively constant and the voltage contains no information. In order to determine the suspension cylinder pressure, the VIMS module measures the frequency of the signal. Calibration of the VIMS truck payload system is required after replacement of the suspension cylinder pressure sensor.
Speed Sensor
 | |
| Illustration 2 | g00482515 |
Speed Sensor | |
The speed sensor sends a signal that is proportional to the engine speed of the 994 to the VIMS module. Because this is a powered sensor, the output voltage is relatively constant and the output voltage does not contain information.
Lift and Tilt Cylinder Oil Pressure Sensor
 | |
| Illustration 3 | g00482517 |
Lift and Tilt Cylinder Oil Pressure Sensor (1) Schematic symbol (2) Sensor | |
Lift and tilt cylinders oil pressure sensor (2) reacts to the pressure that is in the lift cylinder or tilt cylinder. One Lift and tilt cylinders oil pressure sensor is used in each oil circuit. The sensor receives operating power from the machine electrical system. The sensor sends a square wave signal to the VIMS. The square wave signal increases in frequency as the pressure in the suspension cylinders increases. The signal voltage is relatively constant and the voltage does not contain information. The VIMS measures the frequency in order to determine the pressure in the lift cylinders or tilt cylinders. Calibration of the VIMS loader payload system is required after replacement of the lift cylinder oil pressure sensor and tilt cylinder oil pressure sensor.
Resistive Sensors
Fuel Level Sensor - Resistive Type
 | |
| Illustration 4 | g00482519 |
Fuel Level Sender (1) Sender (2) Schematic symbol (3) Pictograph symbol | |
 | |
| Illustration 5 | g00482523 |
Buffer (Fuel Level) (4) Schematic symbol (5) Buffer | |
Fuel level sender (1) and buffer (5) provide a way of sensing the level of the fuel. A resistive signal which corresponds to the depth of the fuel within the fuel tank is sent from sender (1) to buffer (5). Buffer (5) receives operating power from the machine electrical system. The buffer converts the resistive sender signal into a PWM signal which is sent to the VIMS. The VIMS measures the duty cycle of the signal from the buffer in order to determine the level of fuel on large wheel loaders (LWL).
Pulse Width Modulated Sensors (PWM)
 | |
| Illustration 6 | g00482644 |
Pulse Width Modulated Signal | |
 | |
| Illustration 7 | g00482601 |
Typical Schematic of a PWM Sensor | |
Pulse width modulated sensors (PWM) produce a digital signal with a duty cycle that varies as the condition changes. The frequency remains constant.
Temperature Sensor - Fluids And Ambient Air
 | |
| Illustration 8 | g00482655 |
Fluid Temperature Sensor (1) Schematic symbol (2) Sensor | |
Temperature sensor (2) reacts to the temperature of fluids such as hydraulic oil, power train oil, or engine coolant. The sensor receives operating power from the VIMS interface module. The sensor sends a signal that changes as the fluid temperature changes to the main module. The VIMS measures the duty cycle of the sensor signal in order to determine the fluid temperature.
Temperature Sensor - Engine Exhaust Gas
 | |
| Illustration 9 | g00482659 |
Engine Exhaust Gas Temperature Sensor (1) Schematic symbol (2) Sensor | |
Temperature sensor (2) reacts to the temperature of engine exhaust gas. The sensor receives operating power from the VIMS interface module. The sensor sends a PWM signal which changes as the temperature of the engine exhaust gas changes to the main module. The control measures the duty cycle of the sensor signal in order to determine the temperature.
Pressure Sensor
 | |
| Illustration 10 | g00482680 |
Pressure Sensor (1) Schematic symbol (2) Sensor | |
Pressure sensor (2) reacts to system pressure such as system air pressure. The sensor receives operating power from the appropriate interface module. The sensor sends a PWM signal to the VIMS that changes in proportion to the air pressure. The VIMS measures the duty cycle of the sensor signal in order to determine the pressure.
Coolant Loss Sensor
 | |
| Illustration 11 | g00482683 |
Coolant Loss Sensor (1) Sensor (2) Schematic symbol (3) Plastic sleeve | |
The coolant loss sensor is an electronic switch that is activated by coolant. During normal operation, coolant loss sensor (1) is closed to ground. The switch opens when the coolant level is too low. The VIMS module warns the operator of a very low coolant condition in the cooling system when the switch opens. The sensor has a connector with three contacts. Contact "A" connects to the +8 DCV sensor power from the interface module. Contact "B" connects to ground and contact "C" (switch output) connects to the input of the interface module. When the sensor is tested on the bench, the switch is open when power and ground are disconnected. The sensor cannot be tested in this state.
Note: DO NOT remove plastic sleeve (3) from the probe. This plastic sleeve is required for proper switch operation.
The internal electronic switch that is in this sensor functions as a mechanical switch. The switch is either open or the switch is closed to ground. Contact C is closed to contact B. This sensor works with ONLY water or water/glycol solutions (antifreeze). The sensor will not work with oils, fuels, etc. A pull-up voltage must be present at the signal lead. The pull-up voltage is used in order to pull up the open circuit voltage, when a loss of coolant has caused the switch to open. This pull-up voltage (5 VDC) is supplied by the interface module. The pull-up voltage can only be measured with a multimeter when the switch is open. When 5 volts are present on the signal lead during normal operation, the switch is open.
Lift Arm Angle Position Sensor
 | |
| Illustration 12 | g00482241 |
Lift Arm Angle Position Sensor (1) Schematic symbol (2) Sensor | |
The angle position sensor of the lift arm is an input to an interface module (994). The position sensor is mounted near the pivot center of the machines lift arm. This is a Pulse Width Modulated Sensor (PWM). The sensor receives operating power from the machine electrical system. The sensor has an output frequency of 600 Hz. The frequency will remain constant. This sensor continuously generates a PWM signal. The duty cycle varies in proportion to the angle of the lift arm. The interface module receives the duty cycle of the PWM signal. The interface module then measures the duty cycle of the PWM signal in order to determine the angle of the lift arm. the VIMS module uses this information in order to determine the location of the lift arms for use with the loader payload system.
Note: The position angle sensor of the lift arm must be calibrated after replacement. See the Testing and Adjusting, "LPS Calibration" section of this manual for the calibration procedure and see the Testing and Adjusting, "Position Sensor (Lift Arm) - Adjust" section for the adjustment procedure. Be careful not to force rotation of the sensor beyond the mechanical limits. Forcing the rotation of the sensor may cause permanent damage.
Fuel Level Sensor - Ultrasonic Type
 | |
| Illustration 13 | g00482602 |
Fuel Level Sensor - Ultrasonic Type (1) Schematic symbol (2) Float (3) Guide tube (4) Sensor | |
Fuel level sensor (4) reacts to the level of the fuel in the fuel tank. Sensor (4) emits an ultrasonic signal up guide tube (3). The ultrasonic signal is reflected off a metal disk on the bottom of float (2) and the signal returns to the sensor. The sensor measures the travel time of the ultrasonic signal. The travel time includes the time to the float and the time back to the sensor. The sensor also measures the temperature of the fuel in order to compensate accordingly. The status of contact 3of the sensor indicates whether the sensor is used in a deep tank or a shallow tank. Contact 3 should be open for a deep tank that has a maximum depth of 2300 mm (90 inch). Contact 3 should be grounded for a shallow tank that has a maximum depth of 1150 mm (45 inch). The sensor receives operating power from the machine electrical system. The VIMS interface module receives a PWM signal from the sensor that changes as the fuel level changes. The VIMS module measures the duty cycle of the sensor signal in order to determine the fuel level.
Note: The fuel level sensor cannot be bench tested. The sensor must have fuel in guide tube (3) in order to operate properly. The sensor can be tested only while the sensor is installed on a machine. For specifications and test procedures, see the Testing and Adjusting, "PWM Sensor Tests" section.