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If you ever plan to replace or test a resolver, then you need to know the functions of each wire. This can be very difficult to determine without a little knowledge and a voltmeter.
There is an industry standard for resolver wire colors that most manufacturers choose to use. These colors are as follows:
| Wire Color | Red/White | Black/White | Red | Black | Yellow | Blue |
|---|---|---|---|---|---|---|
| Wire Function | Excitation + | Excitation – | Cos + | Cos – | Sin + | Sin – |
Proprietary Wire Colors
Sometimes Yellow/White can be used in the place of Black/White for Excitation. These are industry standard wire colors but you will come across other brands of resolvers with their own proprietary color designations. When this happens you will need to use a voltmeter to assist you in determining wire color versus function.
Determining Circuits
Almost all resolvers have 6 leads. Use a voltmeter to ring out the leads and determine which 3 pairs of wire are circuits. Then record the resistance of each circuit. The Cos and Sin circuit will have the same resistance, so the circuit with the different resistance will be your excitation circuit. If any circuits ring open, or all three circuits have different resistances then your resolver could have a damaged winding and need to be replaced/rebuilt.
These are some basic tips on how to determine a resolvers wiring. In order to continue on and designate exact wire functions on nonstandard wire colors you will need to excite the windings with the proper frequency and use an oscilloscope.
How Can I Excite the Windings?
Before you can determine exact functions of your resolver wires you will need background information concerning the type of output your motor drive or controller is looking for. Most manuals will describe the specific sin and cos outputs used based on the direction rotation. You need this information to proceed.
In order to test your resolver you will need to excite your resolver with the proper voltage and frequency which is typically written on the resolver label. Most resolvers are between 4-6V at 3-10KHz. People who don’t have test equipment that can feed high frequency hook their resolvers to their drive and check the sin and cos outputs either on the drives test points or directly off of the resolver.
Once you have the resolver running on the scope you just need to set up the outputs of the resolver to match the drive/controllers specifications paying attention to the direction of rotation.
Here is a link with some more information on resolver windings:
Advanced Micro Controls: What is a Resolver?
Does the Mechanical Position of a Resolver Matter When Fitting to a Servo Motor?
The angular position of the resolver stator to the resolver rotor is critical. Most resolver stators are mounted in a way that they can be rotated 360 degrees easily in relation to the motor housing with no alignment pin or key. When the resolver stator or rotor is rotated independent of the other, however, the electrical angle of the resolver relative to the servo motor will change and you will lose your proper alignment.
You can rotate the entire resolver as a unit to any physical position relative to the motor. Many resolver manufacturers mark a line from the rotor to the stator to designate 0 degrees. As long as the lines line up you can put the resolver in any position you like and know your resolver is at 0 electrical degrees.
How Can I Determine Rotor to Resolver Position for Correct Commutation Signals to the Servo Drive?
Your best bet is to find documentation on the drive. There is no way to determine the correct alignment with just the motor. The alignment is whatever the drive needs it to be, which varies drive to drive.
Another way to determine the correct alignment is by examining a sister motor. You will need to use your controller or other equipment to determine the angle of the resolver as there is no zero degree mark.
