Crank Angle Sensor:
The Nissan optical trigger sensor is used by almost every ECU controlled Nissan engine. It is a sensor that spins at half the engine speed and is therefore able to measure the engine cycle position. It can be used as a trigger for direct fire and sequential injection applications. The sensor consists of two signals that will from now on be referred to as home and trigger. The trigger signal consists of 360 evenly spaced pulses, where each falling edge represents 2 degrees of engine movement.
The home signal consists of the same number of pulses as the engine has cylinders. so on a 4 cylinder there are  4  pulses, and on a 6 cylinder there are 6 pulses. The rising (leading) edge of each slot is evenly spaced, but the falling [trailing] edge is not evenly spaced (I.e. different sized holes around the inside of the plate to represent different cylinders). The differing pulse width enables the ECU to determine which pulse occurs immediately before cylinder number 1. The ECU does this counting the number of 360 pulses that occur during the trigger pulse.
There are a number of common patterns for Nissan triggers, but for each pattern, there is always a unique window. You do not need to know what the patterns are, but you need to know which unique window size to use for a given sensor. The sizes are described by the number of small teeth that it inside of the window of the large slots.
The unique slot sizes form pairs with two unique slots at opposite ends. Typical patterns are 4,8,12,8 for a 4—cylinder motor. For 6—cylinder motors of tl1is pattern type, typical patterns are 4,8,12,16,12,8, These patterns are found in RB20 motors.
The differences can be seen below in the pictures of most of the sensors.

The change of number can indicate an improvement or update, a different manufacturer etc. As a General rule of thumb, the Hitachi units with the black plug on the base, are fully rebuild-able.(R32-R33)
Despite CAS’s not all being interchangeable, the internals of the units read the same. So therefore someone with a 1989 RB26, can change their exhaust Cam to an R34 item, and solder an R34 CAS plug in place of the original one, and use a 2002 model’s plastic cased CAS. The ECU, will not read the information any differently.

Common CAS trouble shooting:
There are a number of issues, I have come across in the time that I have played with RB’s they include:
Knocking noise coming from CAS: This can occur when you remove the front cover, and run the CAS, a simple fix is to put a couple of washers under 3 bolt holes to space it (obviously being careful not to drop any down the front cover). Sensor can also make a similar noise when the bearings in the unit are on the way out.
Broken Aligning lug on Camshaft or CAS: This is one of the most common problems that occurs when playing with the CAS, it doesn’t take much and allot of the time, you can find either broken when you remove the unit. A simple hint to help prevent this however it before you replace your CAS, put a generous smudge of Grease down the splined drive, not only will it keep it lubricated, but it will reduce heat and movement. When fitting a broken CAS or one to a cam with no lug, look at where the half moon piece was, and generally you can see where the break occurred, i like to make this with a paint marker, so that you have half a chance of lining it up. Generally takes a few goes, but as it is splined, there are only a few places it can line up. So persevere with it. The change of camshaft & release of the 23731-5L300 was to eliminate this problem.
Note - The late R33 RB25 with later CAS, were not a neo engine, but hydraulic lifter cam with later CAS drive.
Dirty contacts/plug: Simply spray with a reputable brand contact cleaner and drain any excess fluid away from plug.