Frequently Asked Question
Background
The EIS uses VDO brand sensors for oil pressure. These sensors vary in resistance corresponding to changes in pressure. There are two types of sensors that might be used with the EIS. The type of sensor must match the type of instrument.
To determine the type of sensor the instrument requires:
The software version (SW Ver) of the EIS contains an “S”, “V” or “J” in the 3rd position that indicates the type of sensor it can use. For example, 44S84F would by an “S” type, where a 44V89F would be a “V” type.
If it is difficult to see this label, a 100 ohm resistor test can be used to determine the type of EIS. To perform this test, remove the oil pressure connection from the airplane's oil pressure sensor, and connect it to a 100 ohm resistor. Ground the other lead of the 100 ohm resistor. A type V or S instrument will read about 75 psi (+/- 10) and a type J will read about 37 psi (+/- 5).
To determine the oil pressure sensor required:
The oil pressure sensor is labeled on the flat of the nut used to tighten the sensor when it is installed.
The “S” and “V” type instruments require the VDO 0-10 bar (150 psi) pressure sensor.
The “J” type instruments require the VDO 0-5 bar (80 psi) pressure sensor.
The EIS measures oil pressure via a variable resistance oil pressure sending unit. The sending unit varies its resistance between its terminal and its case (which is a connection to ground). Its provides 10 ohm resistance at zero oil pressure, and about 1.2 ohms per psi (or about 100 ohms at 75 psi) for the 150 psi sending unit. The 80 psi (5 bar) sending unit is about 2.4 ohms per psi (or about 100 ohms at 38 psi).
Early Model 3 EIS for 4-stroke engines (“Advanced EIS models”), which can be identified by their two 9-pin connectors) include an OilZero setting. This can be used to account for an offset in the oil pressure sending unit. This setting should normally be 0. Set it to 0 before proceeding further.