94DieselSub
Member
OK, here's my take on this filter Harness:
The black device is a Capacitor 22uF (22 microfarad / 25V) looks like an electrolytic, which explains their high failure rate at under-hood temps. This Cap, as stated is strapped across the ECM/PCM 5VDC sensor Ref voltage going to the Optical Sensor. The 1-Ohm resistor is in series, before the Cap. To my knowledge the Optical Sensor is nothing more than a LED based optical-encoder, interfaced to the micro-perforated timing pinwheel. Most LED diodes draw 10-30milliAmps, so the 1-Ohm padding resistor is transparent to the Op-Sensor but provides additional source impedance thus requiring a lower value Cap to obtain the same -3db filter point (Fs3), and establishes a 6db per Octave lowpass filter poll. The 1-Ohm resistor (as previously stated) can also provide some sys protection in a failure mode of the Op-Sensor or the Filter Cap shorting.
This is Not a “clipping” circuit, as in a Zener Diode, MOV, TVS-Transorb, or an active voltage limiting circuit. It’s a cheap/simple power/signal noise filter. As such, one could purchase a small project PCB from RatShack, cut it in four and make four of these “Filters” with some of these Caps “RDEC71E226K3K1C03B” and some 1/2W 1Ohm metal film resistors. Remove filter Harness, cut out rubber slug, solder in your new DIY PCBA, seal with epoxy potting or eqv.:rolleyes5:
The black device is a Capacitor 22uF (22 microfarad / 25V) looks like an electrolytic, which explains their high failure rate at under-hood temps. This Cap, as stated is strapped across the ECM/PCM 5VDC sensor Ref voltage going to the Optical Sensor. The 1-Ohm resistor is in series, before the Cap. To my knowledge the Optical Sensor is nothing more than a LED based optical-encoder, interfaced to the micro-perforated timing pinwheel. Most LED diodes draw 10-30milliAmps, so the 1-Ohm padding resistor is transparent to the Op-Sensor but provides additional source impedance thus requiring a lower value Cap to obtain the same -3db filter point (Fs3), and establishes a 6db per Octave lowpass filter poll. The 1-Ohm resistor (as previously stated) can also provide some sys protection in a failure mode of the Op-Sensor or the Filter Cap shorting.
This is Not a “clipping” circuit, as in a Zener Diode, MOV, TVS-Transorb, or an active voltage limiting circuit. It’s a cheap/simple power/signal noise filter. As such, one could purchase a small project PCB from RatShack, cut it in four and make four of these “Filters” with some of these Caps “RDEC71E226K3K1C03B” and some 1/2W 1Ohm metal film resistors. Remove filter Harness, cut out rubber slug, solder in your new DIY PCBA, seal with epoxy potting or eqv.:rolleyes5: