clutch sensor voltage questions
04-24-2013, 09:53 PM
#1
clutch sensor voltage questions i was finally able to get my rev limiter working by tying into the clutch position sensor (ecu pin 32 gray wire). so when the clutch is in the limiter kicks in. however, i still don't quite understand how that circuit works and need someone with more electronic knowledge to school me!!
with the ignition on and the clutch out, my multimeter shows virtually no voltage on the circuit. i assume the clutch position switch on the clutch is completing the circuit to ground. and with the clutch in, my multimeter shows about 10.5 volts on the circuit. again i assume the clutch sensor has now broken the circuit to ground and when i tap into the wire with my MM that my MM is now completing the ground.
what i don't understand is with the clutch out and the circuit being complete to ground why i am not getting a voltage reading when i tap the wire with my MM. i would assume that there is voltage flowing from the ecu thru the clutch switch to ground so it seems like i should be picking up the 10 - 12 volts, yet i only get a fraction of a volt!?!
with the ignition on and the clutch out, my multimeter shows virtually no voltage on the circuit. i assume the clutch position switch on the clutch is completing the circuit to ground. and with the clutch in, my multimeter shows about 10.5 volts on the circuit. again i assume the clutch sensor has now broken the circuit to ground and when i tap into the wire with my MM that my MM is now completing the ground.
what i don't understand is with the clutch out and the circuit being complete to ground why i am not getting a voltage reading when i tap the wire with my MM. i would assume that there is voltage flowing from the ecu thru the clutch switch to ground so it seems like i should be picking up the 10 - 12 volts, yet i only get a fraction of a volt!?!
04-25-2013, 11:36 AM
#2
A voltmeter does not measure voltage flow because voltage does not flow, current does. Voltage is the difference in electrical potential between two points in a circuit. Current is the flow of electricity between two points with different electrical potential (voltage).
Voltmeters measure the difference in electrical potential between two locations in a circuit. Often one point is a common ground so that the meter measures the potential energy of the positive side as a difference to the ground. The meter can also measure energy use such as when you measure the voltage drop across a resistor to determine how much energy is converted to heat.
When you connect the positive probe to one end of a power wire and the negative to the other end, you will see basically zero volts even though current is flowing because the difference in voltage is almost unreadable (only the voltage drop caused by the resistance of the wire itself, which is tiny).
In this case, you connect the positive probe to the wire and the negative probe to ground. When the switch is open (clutch is depressed) there is no connection to ground so the meter reads the difference between the voltage on the wire and ground... you get a reading of 10+ volts. When the switch is closed (clutch is released) there is a connection directly to ground so there is no difference in electrical potential and you get basically a zero reading. The only reason you see any reading at all is because there is a certain small amount of voltage drop due to the resistance of the wire and the switch.
Voltmeters measure the difference in electrical potential between two locations in a circuit. Often one point is a common ground so that the meter measures the potential energy of the positive side as a difference to the ground. The meter can also measure energy use such as when you measure the voltage drop across a resistor to determine how much energy is converted to heat.
When you connect the positive probe to one end of a power wire and the negative to the other end, you will see basically zero volts even though current is flowing because the difference in voltage is almost unreadable (only the voltage drop caused by the resistance of the wire itself, which is tiny).
In this case, you connect the positive probe to the wire and the negative probe to ground. When the switch is open (clutch is depressed) there is no connection to ground so the meter reads the difference between the voltage on the wire and ground... you get a reading of 10+ volts. When the switch is closed (clutch is released) there is a connection directly to ground so there is no difference in electrical potential and you get basically a zero reading. The only reason you see any reading at all is because there is a certain small amount of voltage drop due to the resistance of the wire and the switch.