Generic Resolvers

The TI-5000JX provides support for resolver check out with built-in resolver hardware (no external adapter module required). The resolver may be connected directly to the TI-5000JX resolver connector, J12. For viewing the resolver signals on an oscilloscope, the TI-3011 Resolver Breakout Board may be plugged into the resolver connector and the resolver connector plugged into the breakout board. The excitation amplitude is adjustable over a range of 0.0 - 8.0V peak, and the excitation frequency is adjustable from 1,000 to 20,000 Hz. in 4 ranges. These settings are made using the Resolver Excitation Setup window as described in a later section.

General Comments

Since a resolver is basically a transformer in which a voltage input to the excitation winding produces a voltage output to the sine and cosine windings, there is a transformation ratio involved due to the number of turns in these windings. The ratio may be checked approximately during setup by comparing the excitation voltage selected during setup, with the Vector Level in the Data Display (see Data Display screen below). This is approximate because the voltages are only expressed to 0.1 V resolution. Another source of error occurs when there is a phase shift between the excitation signal and the sine and cosine signals. The vector level will be reduced if a phase shift exists. For best accuracy, the excitation frequency should be adjusted such that the sine and cosine signals are either in phase or 180 degrees out of phase with the excitation signal. If from experience, you use the same excitation frequency and voltage routinely for a particular type of resolver, a significant difference in vector level reading would warrant further investigation since a change in transformation ratio would not be expected. 

When the angle read from a resolver goes through 360 degrees in a single revolution, that resolver is called a single speed or 1 speed resolver. However, resolvers can have various numbers of poles just like motors. While a 2 pole resolver is referred to as a single speed resolver, a 4 pole resolver is a 2 speed resolver and so on with the speed being the same as the number of pole pairs. The resolver angle reading will go through 360 degrees as many times as the speed. Servo motors will commonly use 1, 2, 3 and 4 speed resolvers. Single speed resolvers are commonly used with any number of pole motors. However, resolvers higher than single speed will normally be used on a servo motor with the same number of pole pairs as the resolver speed. For instance, a 4 speed resolver would normally be used with an 8 pole motor. While this is typical, at least one example is known of an 8 pole motor using a 2 speed resolver. Other kinds of applications (besides servo motors) may use resolvers as high as 36 or more speeds. Servo motors, however, are normally limited to the number of pole pairs of the motor (which is seldom above 6).

The most common problems that cause incorrect results from a good resolver are incorrect connection to
the tester and incorrect excitation. Double check connections and follow the suggestions in the section on connections to ensure that the resolver is connected properly. The most common problems with excitation are excitation amplitude too high or the excitation frequency too low. Both of these situations can lead to waveform distortion, and waveform distortion can result in angle readings that are inaccurate or jumpy, dead spots in the rotation, etc. Follow the procedures in the section on setup to avoid waveform distortion.

The question often comes up as to the effect of reversing various resolver leads. The following table shows the effect of lead reversal, and this makes it clear why simply reversing the sine leads is the least complicated way to change the resolver direction.

In the following table, when we say “reverse sine” we mean to switch the SIN and SIN* resolver leads on the terminal block. When we say “exchange sine and cosine” we mean to connect the resolver SIN and SIN* leads to the terminal block COS and COS* terminals respectively and connect the resolver COS and COS* leads to the terminal block SIN and SIN* terminals respectively.

You can see that the effect of making a combination of changes can be predicted by the individual changes. For instance, reversing the sine leads will reverse the direction. If we then reverse the cosine leads, the direction is reversed again, and the angle is advanced by 180 degrees. The double reversal of direction puts us back to the original direction, and we are advanced by 180 degrees. That is the same thing the table tells us for reversing both the sine and cosine leads.

As an example of applying these rules, we could predict that exchanging the sine and cosine leads and reversing the excitation leads would advance the angle by 270 degrees and reverse the rotation.

Types Supported

The TI-5000JX works with resolvers that accept an excitation input and produce outputs whose amplitudes are proportional to the sine and cosine of the mechanical shaft angle. Multi-speed resolvers are compatible. Their angle indication will simply go through 360 degrees multiple times per revolution. The TI-5000JX is not compatible with synchros that produce outputs whose amplitudes are 120 degrees apart. It is not uncommon for resolvers to be wired to use the Phase Analog method of resolving the mechanical angle. With the Phase Analog method, excitation voltages 90 degrees apart in phase are applied to the sine and cosine windings while the resultant output signal is taken from the stator winding (that would normally be used for excitation). This is more of a method of reading the angle than a different type of resolver, and these resolvers are normally compatible with the TI-5000JX providing they are connected in the conventional manner as described in the next section.

Connection

Resolvers will have excitation input and sine and cosine output leads that must be connected to the TI-5000JX. Insert the TI-3011 Breakout Board into the 7 pin terminal block connector, J12, on the right hand side of the unit, and then insert the resolver connector into the breakout board. The resolver can be plugged directly into J12, but using the breakout board will provide some advantages, especially for an initial connection. The breakout board provides the pin numbers and signal names to make it easy to wire your resolver into the 7 pin terminal block, and it provides a simple way to connect an oscilloscope to observe the excitation, sine and cosine signals to verify clean signals with no distortion.

Note:

1. The excitation voltage measured on the oscilloscope from the EXC testpoint will be half the voltage that is actually applied to the resolver excitation windings. This is due to the fact that the resolver leads are normally connected between EXC and EXC* instead of EXC and GND.
   
   
2. The excitation voltage displayed on the TI-5000JX takes into account the factor of 2, and it should be correct (twice the oscilloscope reading).
   
   
3. The COS* and SIN* are at GND potential, so they should read correctly on the oscilloscope and that should agree with the readings on the TI-5000JX display. The resolver should be connected as follows:
   
   
   
   It is not as important which leads you select for each pin as it is important that you document how you did it. If you have pin configurations from the manufacturer, then you can use their designations. If not, you can make up your own. Either way, you should document how you do it. That will allow you to connect it the same way each time you work on the same type of motor, and any commutation alignment data that you take should be repeatable. Typical resolver lead designations would be as follows:
   
   
   
   If you have no colors to go by or other documentation, you could take resistance readings on the various windings. Normally the sine and cosine windings will be very close to the same resistance, and the excitation winding will be different.

Setup

Setup for the resolver involves setting the commutation amplitude and frequency. This is accomplished by clicking the Resolver Setup button from the Data Display with resolver as the selected feedback.

To ensure proper amplitude and frequency settings, you should connect an oscilloscope to the TI-3011 Breakout Board so that you can observe the excitation, sine, and cosine signals to verify correct levels with good clean sine waves and no distortion. If you have voltage and frequency settings available from previous encounters with a particular resolver, you may not need to observe the waveforms on the oscilloscope and can go right to the desired settings. However, if you get poor readings, you may need to use the oscilloscope to help determine the problem with the resolver.

Resolvers require the following setup sequence with the resolver to be tested already connected:

1. To select resolver feedback, click on the Select Feedback button in Data Display, and then click on the Resolver Feedback radio button in the Select Resolver frame of the Select Feedback window. Click the OK button after the resolver selection has been made.
   
   
2. Click on the Resolver Setup button in the Data Display to bring up the Resolver Excitation Setup window.
   
   
3. Use the Frequency Range dropdown menu to select the range (1, 2, 3 or 4) which corresponds to the desired frequency. The frequency covered by each range is shown on the Instructions/Comments box on the display. The ranges are as follows:
   
   
   
   If you know the frequency specified for your specific resolver or motor, then that will be the frequency that you are selecting. If you do not have that information, you will want to select a frequency which puts the sine and cosine signals either in phase or 180 degrees out of phase with the excitation signal. To look at this phase, you will need to connect an oscilloscope to the TI-3011 Breakout Board as described in the preceding section. When signals are in phase or 180 degrees out of phase, their zero crossings will line up with each other.
   
   
4. When the desired range has been selected, use the Frequency Set Point dropdown menu to select the desired frequency within the selected range. On the bottom line under Set, the frequency setting (in Hz.) will be shown. In the Actual Frequency in Hz. and Actual Frequency in KHz. boxes, the actual measured frequency will be show. The frequency set point and actual frequency numbers will normally be fairly close together, but not exact. If the specified frequency is not available from the menu, just select the closest available frequency, which will be plenty close enough.
   
   Note: If the level is set too low to get a good frequency measurement, you may need to adjust the level as described in the next step and then come back to the frequency adjustment.
   
   
5. Click the Level Set Point dropdown menu and select a voltage in the 2 to 3 V range. Note whether the voltage shown in the Vector Level box is between 1.5V and 3V. If it is not, adjust the Level Set Point up or down to get the vector level in that range. A 2.5 V vector level is a good target.
   
   
6. If the frequency and level adjustments are not where you want them yet, then repeat those adjustments until you have the desired results.

Data Display

Data Display is selected by clicking the Data Display button to read the resolver angle and vector level. The Data Display is the only test available for resolvers.

Resolver angle Readings

The Resolver Angle Readings frame shows the current resolver angle in degrees and Baldor HEX code angle. Unless you have used a Baldor resolver tester in the past and have lockup data recorded in that format, just ignore the Baldor data and use the angle in degrees.

The angle displayed should change in a reasonable manner as the resolver is rotated. For instance if a 1 speed resolver is rotated ¼ revolution, the angle should change by 90 degrees. The angle should change smoothly during the entire rotation.

Resolver Output

The Resolver Output frame shows the resolver output signals described in different ways. The individual sine and cosine voltage levels are shown in the Sine and Cosine boxes respectively. The cosine will reach a positive peak at 0 degrees and negative peak at 180 degrees, while the sine will reach a positive peak at 90 degrees and a negative peak at 270 degrees. The main thing to watch for here is that the peak voltages reached by the cosine and sine outputs are the same, the positive and negative peaks are the same, and the peaks are the same as the vector level. Within 0.1 or 0.2 volts is close enough to consider it the same voltage. If either the sine or cosine signal is zero all the time or never changes, there is a problem with that resolver channel or possibly with the resolver connections to the tester. An ohmmeter check of that winding may reveal a shorted or open winding. If both signals are zero, then there may be a problem in the excitation windings. Again an ohmmeter check may help determine the problem. The ohmmeter will measure the resistance of the excitation winding on the stator. However, this winding is transformer coupled to an excitation winding on the rotor, and the ohmmeter reading will not tell you anything about the rotor winding.

The Vector Level box displays a calculated quantity that, for lack of a better name, we call the vector level. Trigonometry tells us that the square root of the sum of the squares of the sine and cosine of any angle is equal to 1. Since the sine and cosine voltages are proportional to the sine and cosine of the angle, the square root of the sum of the squares of these voltages should equal a constant voltage for an ideal resolver. By computing this vector level from the sine and cosine voltages, we have access to a number that can easily point out problems in resolver signals. As the resolver is rotated, the vector level should not vary by more than a couple tenths of a volt. If it does, then the sine and cosine signals are not consistently at the correct amplitudes. This may mean that there is a problem with the resolver, perhaps the signals coming back from the resolver are distorted, or the excitation level may be too high. Using the breakout board to connect an oscilloscope to the excitation, sine and cosine signals will help determine the problem.

If the sin/cos signals coming back from the resolver are too low and the vector level is below 1.0 V peak, then the Vector Level box background will change to red indicating a low signal problem. From 1.0 V to 1.4V, the background will be yellow indicating marginal levels. From 1.5 V to 2.9 V, the background will be green indicating a good range of levels. From 3.0 V to 3.1 V the background is again yellow to indicate a marginally high level. Levels from 3.2 V and above will show a red background to indicate a high level.  The excitation level must be adjusted into the acceptable range using the setup procedure described in the setup section. If a good range cannot be achieved, then there is likely a problem with the resolver, and an oscilloscope may help in figuring out the problem.

Resolver Excitation Set Points

The Resolver Excitation Set Points frame shows the frequency and level set points, in the Frequency and Amplitude boxes respectively, that were selected in the Setup Window.