Abstract:
An improved method, for obtaining a datum concerning the rotation speed (n) of a rotating object, such as a motor rotor ( 32 ), offers high precision. Typically, the motor has a sensor ( 61 ) which supplies a sensor signal that has, for each revolution of the rotor, a plurality A of events such as pulses or pulse edges which are counted by a microprocessor ( 23 ) associated with the motor. In order to keep the computation load on the microprocessor from increasing as the rotor speed increases, yet maintain high precision, the measurement is done over a full rotation of the rotor, starts at a first signal event ( 176 ), and ends after a third or nth signal event ( 182 ) which happens at the same rotational position as the first signal event.

Description:
FIELD OF THE INVENTION 
     The invention relates to a method for measuring a frequency datum, in particular a rotation speed datum in the context of a motor, and to an apparatus for carrying out such a method. 
     BACKGROUND 
     Digital systems for sensing the rotation speed of a rotating object (“rotor”) relate to the fact that such a rotor generates one or more signals with each revolution, e.g. needle pulses, pulse edges, or the like. These signals will be referred to hereinafter as “events.” The sensing of a rotation speed datum is based on the fact that the time interval between “events” of this kind is measured, or that a count is made of the number of such “events” occurring per unit time. 
     Since the number of such “events” per unit time increases with increasing rotation speed, correspondingly more calculation time is required to process them in a digital system as the rotation speed rises, so that the calculation time available for other processes decreases. 
     SUMMARY OF THE INVENTION 
     It is an object of the invention to make available a new method for measuring a frequency datum, in particular a rotation speed datum in the context of a motor, and an apparatus for carrying out such a method. 
     According to a first aspect of the invention, this object is achieved by calculating interval length over a period of several events or instants. The result thereof is that the measurement of the rotation speed datum begins approximately at the first predefined instant, and an approximate measurement duration is defined by the first predefined instant and the third predefined instant. This approximate measurement duration is not influenced by the rotational velocity of the rotor. The initiation of the calculation of the rotation speed datum, which calculation can be accomplished after the measurement is complete, is thus also approximately determined in time. As a result, a microprocessor or microcontroller (hereinafter “μC”) that, for example, is present is under a uniform load at all rotation speeds, so that sufficient calculation performance is always available for other tasks as well, e.g. controlling the rotation speed. 
     Because, in the course of a measurement, the “events” are sensed during one complete rotor rotation or a plurality of complete rotor rotations, an averaging occurs during measurement of the rotation speed datum. Specifically, if the rotation speed is ascertained by way of a plurality of short measurements, e.g. by measuring during part of a revolution, it is then usually necessary to create a moving average by calculation from multiple measured values. With the invention, on the other hand, an average is obtained without additional calculation, thereby additionally relieving the load on, for example, a μC. And despite the approximate definition of a measurement duration by way of the defined instants, with the method the actual measurement takes place precisely between two events of the sensor signal which are associated with the same rotational position of the rotor, i.e. the rotation speed datum is measured during complete revolutions. This is of interest particularly in the case of rotors which have, in order to generate the sensor at signal, multiple marks at differing angular distances. Thus in the case of a defined measurement, measurement occurs at the same mark, i.e. at the same rotational position of the rotor, so that any differences in angular distance play no part. This results in a highly accurate rotation speed measurement. 
     Another advantageous embodiment of the invention is when the 3rd instant of one measurement is also the 1st instant of a subsequent measurement. A method of this kind continuously measures a rotation speed datum, since the subsequent measurement follows the instantaneous measurement without interruption. In the vicinity of each defined instant, an instantaneous measurement is terminated and a new measurement is begun. If the predefined instants each occur after a time interval T 13  A, then on average a measurement takes place in each case after the time T 13  A. Processing of the measurement, for example in a μC, can thus take place at regular intervals that are independent of the rotation speed. As a result, the load on the μC is uniform at all rotation speeds, so that sufficient calculation time is left over for other tasks, e.g. for commutating an electronically commutated motor or for rotation speed control. 
     Since in this case there is no pause between the individual measurements, this method is particularly suitable if each individual revolution of the rotor must be taken into account for the measurement, as is necessary, for example, with motors having high-precision controllers or with stepping motors. 
     The invention further concerns a method in which the remainder from a first measurement calculation is taken into account when making a subsequent measurement calculation. The result of taking into account, according to the present invention, the remainder in the subsequent measurement is, when the rotation speed is calculated by division, that no rotation speed information is lost by rounding. This results very advantageously in an increase in measurement accuracy, and is highly advantageous in the context of complicated control operations which demand high precision. 
     The refinement at which successive measurements, made at the same rotor position, are compared has proven extraordinarily advantageous in this context, since a method of this kind is particularly tolerant of interference pulses. An interference pulse does cause an error in the instantaneous measurement, but the subsequent measurements are once again correct, although they use a different rotor position than before to sense the measurement duration. 
     An apparatus which includes a programmed-controlled device for processing the signals and making the time interval calculations also allows the aforesaid object to be achieved. 
     The preferred use of a ring counter has the advantage that the stopping point of the one measurement and the starting point of the next measurement are simultaneous because the ring counter is always running, so that no errors can occur due to measurement delay, and any delays resulting, for example, from the simultaneous occurrence of two interrupts are subsequently automatically compensated for. This makes possible both uninterrupted sensing of the rotation speed and an average error in the rotation speed sensing equal to zero, since no bits are lost during the measurement. 
     Further details and advantageous developments of the invention are evident from the exemplary embodiments described below and depicted in the drawings, which are in no way to be understood as a limitation of the invention. 
    
    
     BRIEF FIGURE DESCRIPTION 
     FIG. 1 schematically illustrates a measurement according to the present invention for a rotor having a single mark  80 ; 
     FIG. 2 shows a schematic depiction of a rotation speed calculation function; 
     FIG. 3 shows a schematic depiction of a measurement according to the present invention for a rotor having two marks  81  and  82 ; 
     FIG. 4 shows the pin assignment of a μC used in the exemplary embodiment, specifically of the type PIC 16C72 from MICROCHIP; 
     FIG. 5 shows a circuit diagram showing components of an arrangement according to the present invention; 
     FIG. 6 shows an actual frequency f before and after signal processing; 
     FIG. 7 shows a flow chart with an overview of the entire program; 
     FIG. 8 shows a function register; 
     FIG. 9 shows a state diagram for a measurement method according to the present invention; 
     FIG. 10 shows a schematic diagram of a measurement according to FIG. 9 for a rotor having four marks; 
     FIG. 11 shows a flow chart for a TIMER 0  interrupt function; 
     FIG. 12 shows a flow chart for a Hall interrupt function; 
     FIG. 13 shows a flow chart for a CALC 13  n function for calculating the rotation speed; 
     FIG. 14 shows a flow chart for a RGL function for controlling the rotation speed; and 
     FIG. 15 shows a schematic diagram of a measurement analogous to that of FIG. 3 in which an interference signal S occurs, to explain the operations occurring in that context. Identical or functionally identical parts, appearing in different figures or embodiments, are hereinafter labeled with the same reference characters and are usually described only once. 
    
    
     DETAILED DESCRIPTION 
     Measurement principle 
     FIG. 1 shows a rotor  32  having a mark  80 , and a sensor  61  for mark  80  which serves as a rotor position sensor. Rotor  32  is usually part of a motor M. If the motor is electronically commutated (ECM), it usually has a rotor position sensor  61  that can then also be used for the present invention. Mark  80  is depicted only symbolically and only for didactic purposes, and can be, for example, a specific magnetic marking of rotor  32  that is sensed by a Hall sensor. In that case mark  80  is not visible to the eye. Mark  80  could also, however, be an optical marking, or a cam that actuates a mechanical switch. In most cases magnetic markings are used in an electric motor (cf. rotor  32 ″ in FIG.  10 ). 
     With the aid of mark  80 , sensor  61  detects a sensor signal f. The latter has pulses at points  165 ,  166 ,  167 ,  168 , etc., one revolution of rotor  32  having taken place between each two pulses. The time axis is labeled t. These pulses represent “events” in the rotation of rotor  32 . In FIG. 1, one event (i.e. 1 pulse) is generated for each complete rotor revolution. 
     The rotation speed of rotor  32  is measured, with the aid of rotor position signal f, as follows: At regular intervals T 13  A, a start signal  161 ,  163 , etc. is generated, triggering a new measurement in each case. 
     The start signal at point  161  is followed by pulse  165 , and the start signal at point  163  is followed by pulse  168 . The measurement takes place between points  165  and  168 . What is measured is the number N of pulses of rotor position signal f that occur after  165  up to and including  168  (i.e. in this case N=3), and the time Δt ( 165 - 168 ) required for those pulses. From this, the frequency of rotor position signal f and thus the rotation speed of rotor  32  can be determined. At each of points  165 ,  168  of the measurement, an old measurement is terminated and a new measurement is started. The procedure here is thus such that at the pulse which follows start signal  161 ,  163 , an old measurement is terminated and simultaneously a new measurement is begun. 
     The number N of pulses can be measured, for example, by resetting the value N to zero at the end of each measurement, and then incrementing the value N by 1 at each pulse. Pulse  165  thus has the ordinal number N=0, pulse  166  the ordinal number N=1, etc. 
     The time Δt can be measured, for example, by taking the difference between the time at the start of the measurement, e.g. t( 165 ) at point  165 , and the time at the end of the measurement, e.g. t( 168 ) at point  168 . 
     For example, if t( 165 )=17.7 ms and 
     t( 168 )=87.7 ms, then 
     Δt( 165 - 168 )=87.7−17.7=70 ms. 
     Start signals  161 ,  163 , which occur at fixed intervals T 13  A, create a measurement window. The measurements do not, however, take place exactly in this measurement window, but rather are measured at a suitable point following the respective start signal at which a pulse (“event”) of rotor position signal f occurs. In the case of a measurement at the instant of the respective start signal, the beginning and the end of the measurement would, in the majority of cases, occur at any point between two pulses of sensor signal f. This would result in an inaccuracy in the measurement. If one waits until the next pulse, however, then complete periods between the pulses are measured, resulting in a considerable increase in measurement accuracy. 
     FIG. 2 schematically shows a calculation of rotation speed n in a rotation speed calculation function  170 . Function  170  receives as input, at time intervals whose average duration is T 13  A, the number N of pulses and the time Δt required for that number N. From this, function  170  calculates a rotation speed datum n as the quotient of number N and time Δt: 
     
       
           n=N/Δt   (1) 
       
     
     FIG. 3 shows rotor  32 ′ (of a motor M 13    2 ) having two marks  81  and  82  and rotor position sensor  61 . Marks  81  and  82  are offset approximately 180° mech. 
     Rotor position sensor  61  detects a rotor position signal f with the aid of marks  81  and  82 . Rotor position signal f has pulses as a result of mark  81  (shown in solid white) at points  176 ,  178 ,  180 ,  182 , and pulses as a result of mark  82  (shown in solid black) at points  175 ,  177 ,  179 ,  181 , etc. One complete revolution of rotor  32 ′ takes place between each two “white” pulses and between each two “black” pulses. 
     Since no distinction can be made between the pulses of marks  81  and  82 , it can be stated more generally that one revolution of rotor  32 ′ takes place between each pulse and the next pulse but one, e.g. between N=1 and N=3. 
     The measurement of rotation speed n of rotor  32 ′ is based on the following considerations: 
     Marks  81 ,  82  can never be arranged entirely symmetrically. For example, it is possible that mark  82  deviates a few degrees from the symmetrical position at 180° mechanical (“mech.”) from mark  81  which lies at 0° mech., i.e. is positioned, for example, at 183° mech. This would result, in the case of a measurement that starts, for example, at point  176  (mark  81 ) and ends at point  181  (mark  82 ), in a measurement error, since the measured angular range would not be an exact multiple of 180° mech. 
     To eliminate this problem, in FIG. 3 only complete revolutions are measured in each case, i.e. measurement always occurs between the same type of mark, and thus what is measured is always exactly a multiple of 360° mech. The measurement that begins at  176 , namely after a start pulse  171 , therefore ends not at point  181  but at point  182 , which is the next point following a start pulse  173 , at which, assuming the measurement has started at point  176 , one complete revolution has occurred. 
     This condition can be described mathematically using the so MODULO (mod) function; for example 
     
       
           N  mod 2=0  (2) 
       
     
     means that when the value N is divided by 2, the remainder is 0. Thus for example  0  mod  2 =0,  1  mod  2 =1,  2  mod  2 =0,  3  mod  2 =1, etc. 
     In FIG. 3, at  183  the value “N mod  2 ” appears beneath pulses  175  through  182 , and a measurement ends/starts only, for example, when a measurement is requested by way of a start signal  171 ,  172  and the condition N mod  2 =0 is also met. 
     Stated more generally, the value of N mod  2  at the starting point and stopping point of the measurement should be the same. 
     If the rotor has a number A of markers, then the condition of equation (2) is generally 
     
       
           N  mod  A =0 or 
       
     
     
       
           N  mod  A =const.  (3) 
       
     
     The variable A will hereinafter be labeled MOD 13  f, and equation (3) is then stated as 
     
       
           N  mod MOD 13  f=0 or 
       
     
     
       
           N  mod MOD 13  f=const.  (3a) 
       
     
     Selection of the first marker can be made either by way of a particular signal, or, for example, the first measured event (here  176 ) can arbitrarily be selected as the event having the ordinal number N=0. The explanation relating to FIG. 15 will clarify this even further. 
     In FIG. 3 the measurement thus occurs either, as depicted, is between “white” pulses or, as depicted on the right in FIG. 15, between “black” pulses. In the example of FIG. 3 the measurement is performed between pulses  176  and  182 . Here N=6 pulses are counted, and the time interval between pulses  176  and  182  is ascertained and equals Δt ( 176 - 182 ). From these two values, a rotation speed datum n is then calculated using equation (1). 
     Let it be emphasized once again that in reality there are no “white” or “black” pulses, but that they are a didactic aid for explanation of the invention. 
     FIG. 4 shows an overview of the terminals used for the exemplary embodiment of a μC  23 , in this case of the type PIC 16C72 from the MICROCHIP company. This is an 8-bit processor. It contains a 16-bit timer and an 8-bit timer, two PWM (Pulse Width Modulation) registers, and several interrupt functions. Of course, this processor constitutes only one example, but it has proven successful in the embodiment described. 
     Among the terminals of μC  23  are MCLR  37 , VSS  38 , CLKIN  39 , CLKOUT  40 , Cl  41 , B 5   42 , B 4   43 , VDD  44 , VSS  45 , SDA  46 , and SCL  47 . 
     FIG. 5 shows a circuit diagram of a preferred arrangement with an electric motor M whose rotation speed is to be regulated. 
     The terminals of μC  23  are depicted in FIG. 4, and the corresponding reference characters are again used. Terminal MCLR  37  is connected via a resistor  71  to a positive voltage +5V. Terminals CLKIN  39  and CLKOUT  40  are connected to a quartz oscillator  75  that generates the clock frequency for μC  23 . Terminal VDD  44  is connected to +5V and terminal VSS  45  to ground GND, and a capacitor  77  is located between the two terminals. μC  23  has two timers TIMER 0  and TIMER 1 , as well as a counter for variable INT_CNT_f described below. Parts that are identical or functionally identical to those in FIGS. 1 and 4 retain the same reference characters. 
     Frequency f detected by rotor position sensor  61  (corresponding to the rotation speed of motor M  32 ) passes via a line  29  to a filter FILT  57 , and from there via line  59  to terminal B 5   42  of μC  23 . 
     Motor  32  has an actuator SG  63  which influences the magnitude of the current flowing through motor  32 . 
     Actuator  63  is connected via a line  33  to a voltage +U_B, and a control output SW is conveyed to actuator SG  63  via a line  27  from terminal C 1  of μC  23 , in order to influence the magnitude of the current that flows via SG  63  to motor M. 
     Mode of Operation 
     μC  23  obtains its operating voltage via terminal VDD  44  at +5V and VSS  45  at ground GND. A filter capacitor  77  protects the supply voltage from voltage peaks and dips. Terminals SDA  46  and SCL  47  of MC  23  provide serial transmission of data and can be connected, for example, to an EEPROM or to an external bus (not depicted). 
     Frequency f is supplied by rotor position sensor  61 , which supplies a constant number of pulses per revolution of rotor  32 . A Hall generator or an optical, mechanical, capacitive, or inductive sensor can be used, for example, as rotor position sensor  61 . 
     Filter  57  serves to prepare the edges of frequency f so that when an edge change occurs, a Hall interrupt  630  (FIG. 7) is reliably triggered at interrupt-capable input B 5   42 . Filter  57  can be, for example, an RC element or a Schmitt trigger. If signal f from sensor  61  is suitable, filter FILT  57  can also be omitted. An example of the action of the filter is shown in FIG.  6 . 
     TIMER 0  of μC  23  is used to initiate start signals  171 ,  173  (FIG. 3) for the measurements, by initiating a TIMER 0  interrupt  638  (FIG. 7) at the corresponding points  171 ,  173 , etc. 
     TIMER 1  of μC  23  is used to determine time difference Δt (FIG.  3 ). TIMER 1  is preferably configured as a ring counter. This has the advantage that the ring counter runs continuously, and no bit is lost during a measurement. The result is therefore rotation speed sensing with very high resolution, operating on average with a zero measurement error. At each interrupt, the value of TIMER 1  is read out and stored. A slight measurement delay may occur if two interrupts should ever occur simultaneously, but it will automatically be corrected in the following measurement cycle, since that cycle then automatically becomes slightly too short (because the stop point of the one measurement is identical to the start point of the next measurement) and the next measurement will be started before the current measured values have been analyzed. 
     A control output SW for the rotation speed control system, calculated in μC  23 , is output via terminal C 1   41 , for example as an analog voltage SW, and is conveyed via line  27  to actuator SG  63  which controls the delivery of current for motor M  32 . Actuator SG  63  can be implemented, for example, as an analog longitudinal controller or as a PWM actuator. 
     FIG. 6A shows frequency f before it enters filter FILT  57 , and FIG. 6B shows frequency f after it has been processed in filter FILT  57 . Frequency f in FIG. 6A derives, for example, from a Hall generator, and edges  109  are less steep. 
     Frequency f in FIG. 6B has been processed by filter  57 . Edges  110  are steep, and in μC  23  each of the steep edges  110  can reliably trigger an interrupt  630  (FIG. 7) which hereinafter is called a Hall interrupt. The Hall interrupts correspond here to pulses  165  through  168  of FIG. 1, and  175  through  182  of FIG.  3 . 
     General Configuration of the Overall Program; Function Manager 
     The architecture of the overall program that executes in μC  23  will be described below, followed by a detailed description of the individual subprograms. 
     FIG. 7 shows a flow chart with one possible embodiment of the overall program executing in μC  23 . 
     Shown at the very top are two interrupt routines: Hall interrupt S 631  (FIG. 12) and TIMER 0  interrupt S 639  (FIG.  11 ), which are executed when the respective interrupt  630 ,  638  occurs and which act on the main program via  632 ,  640 . In this context, the priority, i.e. the sequence in which the individual program sections are executed, decreases from top to bottom. The priorities are therefore labeled L 1  through L 7  on the right-hand side, a smaller number denoting a higher priority. L 1  thus has the highest priority. 
     Below the interrupt routines, the main program begins. After motor M has been switched on, an internal reset is triggered in μC  23 . Initialization of μC  23  takes place in S 600 . 
     After initialization, execution branches into a so-called function manager  601 , which begins in S 602 . Function manager FCT_MAN controls execution of the individual subprograms. 
     Those functions which are time-critical and which must be executed at each pass are processed first. These include, for example, a communication function COMM in S 604  which performs data transfer between μC  23  and an EEPROM (not depicted) or bus (data line). S 606  represents any further time-critical functions that may be present. 
     FIG. 8 shows, as an example, a function register  605  in which one bit is reserved for each function of FIG.  7 . 
     In this exemplary embodiment, function register  605  is 1 byte long, and the following request bits for the requestable functions explained below are defined, beginning from the least significant bit (LSB): 
     FCT_XY for any function S 612 ; 
     FCT_CALC 13  n for a rotation speed calculation function CALC 13  n S 616 ; 
     FCT_RGL for a controller function RGL S 620 . 
     The remaining bits  3  through  7  are reserved for further requestable functions that may optionally be integrated into function manager  601 . 
     Rotation speed calculation function CALC_n S 616  (FIG. 7) serves to calculate the actual rotation speed n. Controller function RGL S 620  (FIG. 14) calculates control output SW (FIG. 5) and outputs it to actuator SG  63  of motor M. 
     If a specific requestable function is to be requested by another function or by an interrupt routine, the bit of the requested function in function register  605  (FIG. 8) is set to 1, e.g. FCT_XY=1. The next time function manager  601  (FIG. 7) has not called any other higher-priority requestable function during a pass, the aforesaid function is executed. 
     Once a requested function has been processed, it sets its own request bit back to 0, i.e., for example, FCT_XY=0. This allows longer functions, which cannot be processed in one pass (for example because they require too much time), to be split up and processed in multiple calls. 
     In FIG. 7, after S 606  a check is made, in a predetermined sequence starting with the most important requestable function, as to whether its request bit is set. If that is the case for a function, that function is then executed and the program then branches back to the beginning FCT_MAN S 602  of function manager  601 . The sequence in which function register  605  is checked defines the prioritization of the requestable functions. The higher the location of such a function in function manager  601 , the higher its priority. 
     The manner of operation of function manager  601  will be explained with reference to an example. If the program branches, for example, from S 610  to S 614 , then in S 614  a check is made as to whether function register bit FCT_CALC_n=1, i.e. whether the rotation speed calculation function CALC_n S 616  has been requested, as depicted in FIG.  13 . If so, then execution branches to S 616 , and the rotation speed calculation function is performed. Upon termination, the rotation speed calculation function CALC 13  n S 616  sets request bit FCT 13  CALC 13  n back to 0 (cf. S 374  in FIG.  13 ), and execution branches back to the beginning S 602  of function manager  601 . 
     If a request bit was not set in any of the queries up to S 618 , then execution branches back, without an action, to S 602 ; functions S 604  and S 606 , which are executed each time function manager  601  is run through, are then processed again. 
     The function manager results in optimum utilization of the resources of μC  23 . 
     Measuring Frequency f 
     FIG. 9 shows a state diagram for measuring frequency. The state diagram has four states S 1 , S 2 , S 3 , and S 4 , and six transitions T 1 , T 2 , . . . , T 6 . Each transition is accompanied by an event and an action. 
     Table 1 below shows the associated event and action for each transition, 
     
       
         
               
               
               
             
           
               
                   
               
               
                 Transition 
                 Event 
                 Action 
               
               
                   
               
             
             
               
                 T1 
                 Interrupt due to 
                 Read and store 
               
               
                   
                 edge change in 
                 TIMER1, increment 
               
               
                   
                 signal f 
                 INT_CNT_f 
               
               
                 T2 
                 Interrupt due to 
                 Enable frequency 
               
               
                   
                 TIMER0 after time 
                 measurement 
               
               
                   
                 interval T_A 
               
               
                 T3 
                 Interrupt due to 
                 Read and store 
               
               
                   
                 edge change in 
                 TIMER1, increment 
               
               
                   
                 signal f 
                 INT_CNT_f 
               
               
                 T4 
                 INT_CNT_f mod MOD_f = 0 
                 Calculate t_MEAS_f, 
               
               
                   
                   
                 INT_MEAS_f; start 
               
               
                   
                   
                 CALC_n 
               
               
                 T5 
                 Instantaneous 
                 None 
               
               
                 T6 
                 Instantaneous 
                 Prepare for new 
               
               
                   
                   
                 measurement 
               
               
                   
               
             
          
         
       
     
     The state diagram of FIG. 9 is explained with reference to FIG.  10 . 
     FIG. 10A schematically shows a four-pole permanent-magnet rotor  32 ″ and a rotor position sensor  61 , which here is configured, for example, as a Hall sensor. Rotor  32 ″ has two south poles (S)  35  and  35 ′ and two north poles (N)  34  and  34 ′. Rotor position sensor  61  detects rotor position signal f, which exhibits an edge  110  each time the rotating rotor  32 ′ moves from a north pole (N) to a south pole (S) and vice versa. At each edge  110  (FIGS. 6B and 10A) of signal f, a Hall interrupt  630  is triggered in μC  23  (FIG.  7 ). Four Hall interrupts  630  are thus triggered for each revolution of rotor  32 ″. 
     FIGS. 10B and 10C show an associated diagram with an example of how the measurement of frequency f proceeds. 
     FIG. 10B shows TIMER 0  interrupts  191 ,  193 ,  195  which are each triggered after a time interval T_A (e.g. TA=25 ms) by timer TIMER 0  (in μC  23 ). 
     FIG. 10C shows frequency signal f which is detected by rotor position sensor  61 . At each of points  197 ,  199 , and  201 , the two variables INT_MEAS_f (number of edge changes since the last measurement) and t_MEAS_f (instant of the present measurement) are forwarded to rotation speed calculation function CAL 13  Cn, which is explained below in FIG.  13 . 
     The value INT_MEAS_f is determined with the aid of an edge counter INT_CNT_f (in μC  23 ), which is reset to zero each time a measurement starts and is incremented by 1 at each edge  110 . The value INT_MEAS_f thus corresponds to variable N of FIG.  1  and FIG. 3, i.e. to the number of measured events  110 . 
     t_MEAS_f is determined by way of TIMER 1 , which is preferably configured as a ring counter, making possible uninterrupted sensing of successive values of t_MEAS_f. 
     The numbers indicated in parentheses indicate the respective instant or time range to which the value in question applies. For example, at time  199  the value INT_MEAS_f( 197 - 199 ) which contains the number of edges in the range from  197  to  199 , and the value t_MEAS_f( 199 ) which contains the instant of the measurement at  199 , are transmitted to rotation speed calculation function CALC_n S 616 . For example, the value of INT_MEAS_f( 197 - 199 ) is 8 because eight edges  110  have been counted. 
     FIG. 10D shows the value resulting from the calculation of INT_CNT_f mod  4 . The MODULO calculation using N mod MOD_f was explained in the description of FIG.  3 . In this exemplary embodiment the value N corresponds to the value INT_CNT_f, and the variable MOD_f was set to equal four, since rotor  32 ″ is configured with four poles, meaning that a number A=4 events  110  occur with each revolution. As depicted in FIG. 10D, the value of INT_CNT_f mod  4  changes, at each edge  110  of signal f, in the sequence 0, 1, 2, 3, 0, 1, 2, . . . , as soon as the motor is switched on. 
     Frequency measurement will now be explained with reference to FIG. 9, the table in the description of FIG. 9, and FIG.  10 . 
     At instant t=0 selected arbitrarily in FIGS. 10B and 10C, the frequency measurement depicted in FIG. 9 is in state S 1 . 
     At each edge  110  (FIG. 10A) of f, a Hall interrupt  630  (FIG. 7) is triggered. This has the following results: 
     Hall interrupt routine S 631  (FIG. 12) is initiated by Hall is interrupt  630 ; 
     in Hall interrupt routine S 631 , counter INT_CNT_f for the number of edges  110  is incremented by 1 (S 322  in FIG.  12 ); 
     in Hall interrupt routine S 631 , the instantaneous value of ring counter TIMER 1  is stored (S 322  in FIG.  12 ). 
     In the state diagram (FIG.  9 ), this is depicted as transition T 1  from state S 1  to S 1 . The event here is a Hall interrupt  630  triggered by an edge  110 , and the action consists in the counting of edge  110  in edge counter INT_CNT_f and storage of the instantaneous value of ring counter TIMER 1 . 
     Another event triggers transition T 2  from state S 1  to state S 2 . The event is the occurrence of a TIMER 0  interrupt initiated by timer TIMER 0 . Timer TIMER 0  initiates a TIMER 0  interrupt  638  at predefined intervals T_A (FIGS. 1,  3 ,  10 B), e.g. at points  191 ,  193 ,  195 . In the associated TIMER 0  interrupt routine S 639  (FIGS.  7  and  11 ), frequency measurement is enabled. Timer TIMER 0  thus defines successive windows with a width T_A. 
     The actual measurement of INT_MEAS_f and t_MEAS f is intended to take place from state S 2 . 
     As FIG. 10 shows, the respective measurement does not take place exactly at instants  191 ,  193 , and  195  of the request, but rather at a suitable instant that is usually somewhat later. 
     In state S 2 , edges  110  of signal f continue to be sensed, and at each edge  110  a transition T 3  (analogous to T 1 ) occurs from S 2  to S 2 , in which the instantaneous value of ring counter TIMER 1  is read out and stored, and edge counter INT_CNT_f is incremented. 
     Final measurement of the values INT_MEAS_f and t_MEAS_f requires that one further condition be met. As explained in the description of FIG. 3, the marks that are applied to rotor  32 ″, i.e. in this case the changes in magnetization from north to south, are not always arranged symmetrically on rotor  32 ″. It is therefore advantageous always to measure at the same mark, thus ensuring that measurement occurs at the same point on rotor  32 ″. 
     The number of edges  110  of signal f is counted in the variable INT_CNT_f; as defined by equation (3), the condition that (in the case of a four-pole rotor) measurement always occurs at a multiple of complete revolutions is achieved with 
     
       
         INT_CNT_f mod  4 =0  (4) 
       
     
     or alternatively with 
     
       
         INT_CNT_f mod  8 =0; 
       
     
     in the latter case, measurement always occurs at the earliest after two complete revolutions or a multiple thereof. If INT_CNT_f mod  12 =0, measurement occurs at the earliest after three complete revolutions, etc. This would, however, degrade the dynamics of a controller. 
     With a measurement at the earliest after one complete revolution, the variable INT_CNT_f mod  4  therefore must have the same value at each measurement. Usually this will be a value of zero, since then with a six-pole rotor measurement can be performed using mod  6  (or mod  12 ), with a four-pole rotor using mod  4  (or mod  8 ), and with a two-pole rotor using mod  2  or mod  4 , so that only the corresponding parameters  12 ,  8 ,  6 ,  4 , or  2  need to be entered into μC  23  in order to readjust it for a different motor. 
     FIG. 10D indicates the result of INT_CNT_f mod  4  for the respective edge. After the measurement is requested at point  193 , for example, edge  199 , which is the eighth edge after point  197 , is then the first edge at which the condition INT_CNT_f mod  4 =0 of equation (4) is met ( 8  mod  4 =0), and a measurement therefore takes place at point  199 . 
     Thus if the number of edges is a multiple of MOD_f, in this case MOD_f=4, then in FIG. 9 a transition T 4  takes place from S 2  to S 3 , the number of edges sensed since the last measurement (which is stored in INT_CNT_f) is stored in INT_MEAS_f (S 330  in FIG.  12 ), and the instant of the present measurement is stored in t_MEAS_f (S 330  in FIG.  12 ). The values INT_MEAS_f and t_MEAS_f are then transferred to the rotation speed calculation function CALC_n S 616 , as depicted in FIG. 13 (cf. S 370  therein). 
     From the present value t_MEAS_f( 199 ) and the stored value t_MEAS_f( 197 ) of the last measurement, it is possible to determine the time Δt_MEAS_f( 197 - 199 ) that was required for the edges counted in the variable INT_MEAS_f( 197 - 199 ). 
     An alternative possibility for determining the time Δt_MEAS_f is to reset the time to zero each time a measurement begins. This can be done, for example, by setting timer TIMER 1  to zero. At the end of the measurement, the time in TIMER 1  corresponds to the value Δt_MEAS_f. INT_MEAS_f and Δt_MEAS_f (cf. FIG. 2) are thus directly present at points  197 ,  199 , and  201 . A disadvantage of resetting timer TIMER 1  is the fact that it then cannot readily be used simultaneously for other measurements. 
     From state S 3  (FIG.  9 ), in which the last measurement is completed, an instantaneous transition T 5  leads to state S 4  in which a new measurement begins. 
     From state S 4 , an instantaneous transition T 6  leads to state S 1 , and the frequency measurement is once again in its initial state S 1 . During T 6 , the next measurement is prepared. For example, counter INT_CNT_f (for the number of edges  110 ) is reset to zero (S 330  in FIG.  12 ). 
     The measurement process as described in FIGS. 9 and 10 has several advantages. 
     With interrupt-based measurements, what is generally done in order to determine the rotation speed is to measure, either at each interrupt or after a fixed number of interrupts, the time since the previous interrupt, and from that to calculate the rotation speed. As a result, an increase in rotation speed means that new measured values arrive more and more often and must be processed. At very high rotation speeds this would result in an overload of μC  23  and a failure to account for individual measured values. 
     With the present measurement method, a new measurement is initiated in each case at predefined intervals T_A. μC  23  is thus under the same load at all rotation speeds or frequencies. 
     The present method furthermore has the advantage that when signal f is measured, measurement occurs at least until the next interrupt. Measurement thus does not occur at simply any instant, for example in between two edges  110 , but rather measurement always takes place from edge to edge, i.e. from event to event, which considerably increases measurement accuracy (cf. FIG.  10 ). 
     A further increase in accuracy is achieved by measuring a multiple of MOD_f edge changes in each case, since this eliminates, for example, measurement errors caused by magnetization faults in a permanent-magnet rotor or by symmetry errors in an externally delivered frequency. This means, for example in the case of a four-pole motor, that a measurement is performed at the earliest at the fourth, eighth, 12th, etc. edge change, in other words whenever INT_CNT_f mod  4 =0. (In a four-pole motor, four edges  110  are generated per revolution.) 
     For this type of measurement with a rotor position signal f having a fixed number A of events (pulses in FIG. 3, edges  110  in FIG. 10A) per revolution of rotor  32 ″, MOD_f is set to equal that fixed number A, so that measurement occurs, after one complete revolution in each case, at the same position of rotor  32 ″. Measurement thus always occurs at the event which is generated at a specific rotor position of rotor  32 ″. It is not necessary for this purpose that there be a particular event which is detected by rotor position sensor  61  and at which it is recognized that one complete revolution has occurred. Instead, all the events in each revolution of rotor  32 ″ can be identical, since the measurement of complete revolutions is accomplished automatically because of the particular measurement approach using MOD_f. 
     This measurement approach is similarly suitable for measuring a frequency signal f that is delivered to μC  23  from an external frequency generator. Such signals f may also have asymmetries during one period of frequency f if, for example, a zero transition at half the period is slightly shifted, so that, for example, a measurement using mod  2  or mod  4  may be advantageous and may yield more accurate results. 
     FIG. 15 shows a rotor  32 ′ having two marks  81  and  82  and rotor position sensor  61 , similarly to FIG.  3 . Rotor position signal f has events in the form of pulses at points  217 ,  218 ,  219 , . . . ,  228 . The pulses are alternatingly generated by white mark  81  and black mark  82  when they rotate past rotor position sensor  61 , and are therefore depicted as white and black for better comprehension. In addition, an interference pulse S occurs between pulses  220  and  221 . Also depicted are control signals  211 ,  213 , and  215  for requesting a measurement. 
     Below the pulses, the value of counter N for the number of pulses is indicated in row  232 , and the result of the calculation of N mod  2  is shown in row  230 . 
     A measurement normally ends/begins whenever a measurement is requested by a control signal  211 ,  213 , or  215  and additionally the value of N mod  2  is equal to zero, i.e. when rotor  32 ′ has rotated an integral multiple of one revolution since the last measurement. 
     The effect of interference pulse S is that for the measurement in the period Δt( 218 - 223 ), it is assumed that rotor  32 ′ has traveled one complete revolution between pulses  220  and  221 , although it has completed only half a revolution. As a result, after control signal  213 , measurement occurs not at the “white” signal  222  but at the “black” signal  223 , since after interference pulse S, N mod  2  now has a value of zero not at the “white” pulses but at the “black” pulses. 
     Measurement is already proceeding correctly again in the following period t( 223 - 227 ), however, since now measurement is taking place in each case at “black” pulses. What has occurred as a result of interference pulse S is therefore a shift in the position of rotor  32 ′ at which measurement takes place. The same would be true if a pulse were missing. The measurement method therefore continues to operate correctly after an erroneous signal S, and continues to measure a multiple of a complete revolution. This constitutes an important advantage of this embodiment. 
     Flow Charts for Measurement of f 
     FIGS. 11 and 12 show flow charts pertaining to a program for the measurement described in FIGS. 9 and 10. 
     FIG. 11 shows TIMER 0  interrupt routine S 639  (FIG. 7) which requests, after each time T_A (FIG.  10 ), the frequency measurement that subsequently takes place in Hall interrupt routine S 631 . 
     The following variables are used: 
     CNT_T_A Internal counter for time T 13  A 
     T_A_TIME Limit value for new measurement 
     DO_MEAS_f Flag to call the frequency measurement 
     TIMER 0  interrupt routine S 639  is performed at every occurrence of a TIMER 0  interrupt  638  (FIG.  7 ). 
     In S 352 , any further steps not set forth here are performed, for example if other program sections are to be controlled by timer TIMER 0 . 
     A subtimer_T_A begins in S 354 . “Subtimer” means that as a result of steps S 356 , S 358 , and S 362  explained below, the actual action in S 360  is triggered only after a specific number of TIMER 0  interrupts. This has the advantage that timer TIMER 0  can also be used for other purposes which need to be called more often. 
     In S 356 , internal counter CNT_T_A is incremented by 1. 
     In S 358 , a check is made as to whether counter CNT_T_A is greater than or equal to the value T_A_TIME. 
     If not, execution then branches immediately to end S 364 , and the TIMER 0  interrupt routine is exited with the instruction “RETI.” 
     If, however, it is found in S 358  that counter CNT_T_A has reached the value T_A_TIME, then in S 360  DO_MEAS_f is set to 1. 
     DO 13  MEAS_f=1 informs Hall interrupt routine S 631  (FIG. 12) that a measurement of frequency f is to be started. 
     The call in S 360  takes place, for example, every 25 ms if the TIMER 0  interrupt is triggered every  10  μs and the value of T_A_TIME=2500. 
     Time T_A must be adapted to the particular motor. For example, if rotor position sensor  61  yields a large number of events with each revolution of rotor  32 , and if rotor  32  is rotating quickly, then T_A can be made shorter. If rotor  32  is rotating slowly, however, then T_A must be set longer, for example TA=250 ms. 
     In S 362 , counter CNT_T_A is reset to zero so that subtimer Subtimer_T_A can be restarted. 
     In FIG. 10, S 360  is called at points  191 ,  193 , and  195 . 
     FIG. 12 shows an exemplary embodiment of Hall interrupt routine S 631  which is executed at each Hall interrupt  630  triggered by the occurrence of an edge  110  (FIG. 4B) of signal f. 
     A This interrupt is so called because it is usually initiated by the signal of a Hall generator  61  (in motor M  32 ). Of course it could also be triggered by an optical or mechanical sensor, and it could also be referred to as a sensor-controlled interrupt. 
     The following variables are used: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 INT_CNT_f 
                 Interrupt counter for sensing the edges of signal f 
               
               
                 INC_f 
                 Increment value 
               
               
                 t_END_f 
                 Instant of the last interrupt of the sensing process 
               
               
                 MOD_f 
                 Number of interrupts for mod calculation, cf. 
               
               
                   
                 equations (3) and (3a) 
               
               
                 t_MEAS_f 
                 Measured time of the last interrupt 
               
               
                 INT_MEAS_f 
                 Number of measured interrupts since the last 
               
               
                   
                 measurement 
               
               
                 DO_MEAS_f 
                 Flag to call the frequency measurement 
               
               
                 FCT_CALC_n 
                 Function register bit of CALC_n function S616 
               
               
                   
               
             
          
         
       
     
     Any desired steps can be performed in S 302 . 
     In the case of an electronically commutated motor, Hall interrupt routine S 631  provides electronic commutation in COMMUT S 304 . This is omitted in the case of a collector motor. 
     Sensing and measurement of signal f begins in MEAS_f S 320 . In S 322 , interrupt counter INT_CNT_f—which is, for example, 1 byte long—is incremented by the value INC_f, e.g. INC_f=1, and the value t_TIMER 1  of ring counter TIMER 1  is stored in t_END_f. Thus both the number of interrupts and the instantaneous time are sensed. 
     In S 324 , INT_CNT_f mod MOD_f=0 is used to check whether the value in interrupt counter INT_CNT_f is a multiple of MOD_f. If MOD_f=4, for example, INT_CNT_f=20 is a multiple of MOD_f, i.e. 20 mod  4 =0. If INT_CNT_f is not a multiple of MOD_f, then execution branches to end S 334  of the interrupt routine. If INT_CNT_f is a multiple of MOD_f, then a check is made in S 326  as to whether DO_MEAS_f=1, i.e. whether a measurement of frequency f was requested in step S 360  of TIMER 0  interrupt routine S 639  (FIG.  11 ). If not, then no measurement needs to be made yet, and execution branches to end S 334 . If so, then in S 328  a check is made on the basis of function register bit FCT_CALC_n as to whether the last rotation speed calculation is already complete. If FCT_CALC_n=1, then execution branches to end S 334 . This prevents measurements from being lost if rotation speed calculation function CALC 13  n S 616  requires too much time. This special situation does not occur in normal operation. 
     In S 330 , variables t_MEAS_f and INT_MEAS_f are set, and are transmitted to rotation speed calculation function CALC_n S 616  that is described with reference to FIG.  13 . 
     For this purpose, t_MEAS_f is set to the most recently sensed timer value t_END_f of ring counter TIMER 1 , INT_MEAS_f is set to the value of interrupt counter INT_CNT_f, and INT_CNT_f is reset to zero. 
     In S 332 , rotation speed calculation function CALC_n S 616  (FIG. 13) is requested by setting FCT_CALC_n to 1, and the measurement request is reset by resetting DO_MEAS_f to zero. 
     TIMER 0  interrupt routine S 639  (FIG. 11) and Hall interrupt routine S 631  (FIG. 12) thus together bring about a frequency measurement as described in FIG.  9 . If μC  23  cannot manage the mod operation, there are other possibilities. 
     In many μCs, an integral division with the instruction “div” yields as its result both the integral quotient and the nonnegative remainder. For example, 7 div 4 yields as its result a quotient 1 and remainder 3. With PCs of this kind, the div operation can be used to calculate the remainder, and measurement, then occurs only at instants at which the remainder has the same value. 
     Another possibility for calculating X mod MOD_f involves, for example, the use of a further variable MOD_CNT, which is also incremented each time variable X is incremented, and which is reset to zero when MOD_f is reached. The MOD_CNT variable then indicates the result of X mod MOD_f. 
     FIG. 13 shows the routine CALC_n S 616  that is requested by the Hall interrupt routine (S 332  in FIG. 12) after measuring timer value t 13  MEAS 13  f and the number of edges  110  (FIG. 4) of signal f in INT_MEAS_f. 
     The following variables are used: 
     
       
         
               
               
             
           
               
                   
               
             
             
               
                 Δt_CALC_f 
                 Time difference since last measurement 
               
               
                 t_OLD_f 
                 Instant of last measurement 
               
               
                 t_MEAS_f 
                 Instant of present measurement 
               
               
                 INT_CALC_f 
                 Number of interrupts since last measurement for 
               
               
                   
                 the calculation 
               
               
                 INT_MEAS_f 
                 Transferred number of interrupts since the last 
               
               
                   
                 measurement 
               
               
                 n 
                 Rotation speed of motor M 
               
               
                 REM_n 
                 Remainder of integral division 
               
               
                 const_f 
                 Factor for parameterization of INT_CALC_f 
               
               
                 REM_n_OLD 
                 Remainder resulting from integral division of last 
               
               
                   
                 calculation 
               
               
                   
               
             
          
         
       
     
     In S 370 , the difference between timer value t_OLD_f of the last measurement and the present timer value t_MEAS_f is calculated and is stored in variable Δt_CALC_f, which corresponds to the value Δt_MEAS_f of FIG.  10 . 
     With ring counters, the difference is usually calculated using the two&#39;s complement. The present timer value t_MEAS_f is then stored for the next measurement in t_OLD_f, and the measured number of interrupts INT_MEAS_f is stored in INT_CALC_f. 
     In S 372 , rotation speed n is calculated. It is proportional to the quotient of the number of interrupts INT_CALC_f (an indication of the number of revolutions) and the time Δt_CALC_f required for them. The applicable equation is: 
     
       
           n =const_f*INT_CALC_f/Δt_CALC_f  (5) 
       
     
     where const_f is a proportionality constant. 
     Interrupt counter INT_CALC_f—which in this exemplary embodiment is, for example, 4 bytes long—is multiplied by const_f. 
     Constant const_f can be selected so that the result of the division in S 372  makes optimum use the range of value n, which for example is two bytes or 16 bits long. This can be achieved, for example, by selecting const_f such that when the number of pulses at maximum rotation speed is divided by measurement window time T_A, the rotation speed assumes a value of approximately 2 15  (if the value of n is 16 bits). This yields high accuracy, but rotation speed n does not correspond to rotation speed n 13  phys measured in RPM. 
     If rotation speed n must correspond to rotation speed n_phys measured in RPM, then const_f must be defined as 
     
       
         const_f=60*TF/MOD_f  (6) 
       
     
     where TF is a time factor constituting the reciprocal of the time unit of ring counter TIMER 1  in seconds. For example, if the time unit of timer TIMER 1  is 1 μS=10 −6  S, then TF is set at 10 6 . For a four-pole motor M with MOD 13  f=4 and TF=10 6 , the result is, for example, const_f=15,000,000. 
     An integral division div, which produces as its result the integral quotient n and positive remainder REM_n, is used to calculate rotation speed n. For a description of the div operator, cf. the explanations of FIG.  10 . 
     A calculation of the rotation speed for the region between points  197  and  199  in FIG. 10 is shown below as an example: 
     INT_MEAS_f is one byte long, INT_CALC_f four bytes, and t_CALC_f two bytes. 
     INT_MEAS_f( 197 - 199 ) has a value of 8, i.e. eight edges  110  of the Hall signal (FIG. 10A) have been counted since the last measurement at instant t_MEAS_f( 197 ). In S 370 , INT_CALC_f has assigned to it the value INT_MEAS_f( 197 - 199 )=8. In S 372 , INT_CALC_f is multiplied by const_f=15,000,000, and acquires the value 120,000,000. 
     The value of Δt_MEAS_f( 197 - 199 ) is, for example, 26,700, which corresponds (if ring counter TIMER 1  has a resolution of 1 μs) to a time of 26.7 ms. In S 370 , Δt_CALC_f has assigned to it the value Δt 13  MEAS 13  f( 197 )=26,700. 
     Dividing INT 13  CALC_f by Δt_CALC_f yields a rotation speed n=4494 and a remainder REM n=10,200. 
     The “physical” rotation speed n_phys corresponds to the number of revolutions per minute. Eight Hall transitions divided by 4 Hall transitions per revolution (four-pole rotor) equals two revolutions, and the time required for them is 0.0267 s. This yields a physical rotation speed n_phys=2/0.0267=74,906 revolutions per second=4494.4 RPM. 
     The calculation also takes into account the remainder REM_n_OLD of the previous rotation speed calculation, by addition to the product of INT_CALC_f and const_f. 
     In the above example, for instance, the calculated rotation speed n exhibits a discrepancy because division yields the integer 4494 rather than the actual result of approx. 4494.4. The difference is not lost, however, but rather is taken into account during the next division in S 372  by adding remainder REM_n_OLD of the last division to the numerator. 
     The advantageous result of taking into account remainder REM_n_OLD is that no information is lost, and there is a measurable improvement in the controller, if one is used. 
     After the calculation of n and REM_n, in S 372  remainder REM_n is stored in REM_n_OLD for the next calculation. 
     In S 374 , function register bit FCT_CALC_n (FIG. 8; FIG. 12, S 332 ) is reset to zero because the rotation speed calculation is complete, and the controller function is requested with FCT_RGL=1. 
     Execution then branches back to the beginning S 602  of the function manager (FIG.  7 ). 
     Controller Function RGL 
     FIG. 14 shows, as an example, a flow chart for an exemplary embodiment of controller function RGL S 620  (FIG. 7) that calculates, from rotation speed n and from a desired rotation speed n 13  s, a control output RGL_VAL which it then outputs. 
     The following variables are used: 
     
       
         
               
               
               
             
           
               
                   
                   
               
             
             
               
                   
                 RGL_DIFF 
                 System deviation 
               
               
                   
                 RGL_PROP 
                 Proportional component 
               
               
                   
                 RGL_P 
                 Proportional factor 
               
               
                   
                 RGL_INT 
                 Integral component 
               
               
                   
                 RGL_I 
                 Integral factor 
               
               
                   
                 RGL_VAL 
                 Control output calculated by controller 
               
               
                   
                 RGL_MAX 
                 Maximum control output 
               
               
                   
                   
               
             
          
         
       
     
     In S 530 , system deviation RGL_DIFF is calculated as 
     
       
         RGL_DIFF=n 13  s 13  n  (7) 
       
     
     S 532  represents a PI controller. 
     Proportional component RGL_PROP is calculated by multiplying system deviation RGL_DIFF by proportionality factor RGL_P. 
     The new integral component RGL_INT is calculated by adding the previous integral component to system deviation RGL_DIFF multiplied by integral factor RGL_I. Integral component RGL_INT preferably has sufficient memory available to it that no system deviation information is lost. 
     Control output RGL VAL is obtained from the sum of proportional component RGL_PROP and integral component RGL_INT. 
     In steps S 534  through S 540 , a range check of control output RGL_VAL is performed. 
     If control output RGL_VAL in S 534  is less than zero, then it is set to zero in S 536 . 
     If control output RGL_VAL in S 538  is greater than the maximum permissible value RGL_MAX, then it is set to RGL_MAX in S 540 . 
     If the value of RGL_VAL lies within a permissible range, it is used unchanged. 
     In S 542 , register SW of a μC-internal D/A converter is set to the value of control output RGL_VAL, and signal SW is output to actuator  63 . 
     Controller function S 620  has thus been performed, and function register bit FCT_RGL is reset in S 544 . Execution then branches back to start S 602  of the function manager (FIG.  7 ). 
     Many modifications and variants are of course possible within the context of the present invention. For example, the present invention can also be used in the context of other controllers, or even without a controller, for measurement of a rotation speed or a frequency that is delivered in the form of a pulse train. The invention was described in conjunction with an electric motor because that constitutes a preferred application, but it is suitable in identical fashion for internal combustion engines, turbines, etc.