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Feedback system, overtemperature protection and termistors
The internal motor feedback system uses a position sensor that outputs a signal telling the controller where the motor is and how fast it is moving. Type of servo controller and motor application are two factors that determines what feedback to use. HDD servo motors can be ordered with a variety of feedback systems, resolver, or encoder with either EnDat or Hiperface protocol. You can find a selection of feedback possibilities in the table below.
As a standard, HDD motors are equipped with over temperature protection. The protection consists of three PTC thermistors in series, one for each phase. The PTC thermistors are manufactured according to norms DIN 44081 and DIN 44082. According to these norms, the resistance for a single thermistor at room temperature is in the range of 20 Ohms – 250 Ohms. For three thermistors in series, the total room temperature resistance is typically between 150 Ohms – 300 Ohms (50 Ohms – 100 Ohms per thermistor). It can be as high as 750 Ohm without indicating malfunction.
The PTC thermistors have a switch temperature of 150 C. When T < 145 C, R < 550 Ohm for each thermistor (R < 1650 Ohms for the whole triplet), and when T > 155 C, R > 1330 Ohm for each thermistor (R < 4990 Ohms for the whole triplet). The resistance should be measured with a d.c. voltage no greater than 2.5V. More detailed information about the PTC resistors can be found here.
As an option, HDD motors can be equipped with a temperature measurement device of type KTY84-130. Detailed information about this device can be found here. The resistance of the KTY device depends continuously on the temperature, as described in the document KTY84-130 that can be downloaded on the left side.
Table feedback system
| Name | Feedback type | Description | Information |
| A | Resolver | 7 V input, 1 pole pair, 0.5 transf. ratio | |
| D | Resolver | 9 V input, 1 pole pair, 0.3 transf. ratio | |
| EC | Endat 2.1 singleturn | 32 lines (19 bits) per rev. | ECI 119 |
| ED | Endat 2.2 singleturn | 32 lines (19 bits) per rev. | EBI 135 |
| EE | Endat 2.2 singleturn, SIL2 | 25 bits per rev. | ECN 1325 |
| EF | Endat 2.2 multiturn, SIL2 | 25 bits per rev. | ECN 1337 |
| EH | Endat 2.2 | 32 lines (19 bits) per rev. | ECI 119 |
| EM | Endat 2.1 multiturn | 512 lines per rev. | EQN 1325 |
| EN | Endat 2.1 multiturn | 2048 lines per rev. | EQN 1325 |
| EO | Sincos, commutation signal | 2048 lines per rev. | ERN 1387 |
| EP | Endat 2.2 battery buffered multiturn | 18 bits per rev. | EBI 1135 |
| EQ | Endat 2.1 singleturn | 18 bits per rev. | ECI 1118 |
| ES | Endat 2.1 singleturn | 512 lines per rev. | ECN 1313 |
| ET | Endat 2.1 singleturn | 2048 lines per rev. | ECN 1313 |
| EV | Endat 2.2 singleturn | 19 bits per rev. | ECI 1319 |
| EW | Endat 2.2 multiturn | 19 bits per rev. | EQI 1331 |
| EY | Endat 2.2 singleturn | 18 bits per rev. | ECI 1118 |
| SS | Hiperface Sincos singleturn | 1024 lines per rev. | Electrically equivalent to SRS50 |
| SM | Hiperface Sincos multiturn | 1024 lines per rev. | Electrically equivalent to SRM50 |
| SC | Hiperface Sincos singleturn 50mm hollow shaft | 64 lines per rev. | Electrically equivalent to SEK90 |