GB2043376A

GB2043376A - A method and circuit arrangement for the digital measurement of temperature

Info

Publication number: GB2043376A
Application number: GB8001448A
Authority: GB
Original assignee: Diehl GmbH and Co
Current assignee: Diehl Verwaltungs Stiftung
Priority date: 1979-02-16
Filing date: 1980-01-16
Publication date: 1980-10-01
Also published as: GB2043376B; FR2449276B3; FR2449276A1; DE2905882C2; DE2905882A1

Abstract

In a digital temperature measurement system, in which a respective value of a temperature-dependent measuring resistor 2 is converted into a pulse repetition frequency, clock pulses 8 which occur during a gate pulse of length dependent on the measured temperature are counted 16, and the counting result is indicated 19 as a temperature value. A number of measuring pulses corresponding to a measurement of 0 DEG are suppressed and the difference between the number of the measuring pulses which occur at any other temperature and the number of suppressed measuring pulses corresponds to the numerical value of that temperature. As shown, the frequency of a multivibrator 1 is controlled by resistor 2 and a gate pulse is applied to AND-gate 7. Logic 9-15 effects the required pulse suppression. Temperatures lying both below and above 0 DEG may be detected. <IMAGE>

Description

SPECIFICATION A method and circuit arrangement for the digital detection of a temperature The invention relates to a method for the digital detection of a temperature, and to a circuit arrange mentforcarrying out such a method. There is described herein a method, for the digital detection of a temperature, in which the respective resistance value of a temperature-dependent measuring resistor is converted into a pulse repetition frequency and in which measuring pulses which occur during a gate pulse and which are dependent upon the pulse repetition frequency are counted and the counting result is indicated as a temperature value.

A method of this kind can be gathered from the house publication "Applications of the 9400 voltage to frequency frequency to voltage converter, AN-10", January 1978, page 2, Teledyne Semiconductor. There a temperature-dependent measuring resistor is provided in a bridge circuit, in which respect an amplifier lies in the bridge branch. The respective temperature-dependent output voltage of the amplifier is converted into a pulse repetition frequency. During gate pulses which are derived from the mains, the measuring pulses which are dependent upon the pulse repetition frequency are counted. The counting result is indicated and represents the temperature value occurring at the measuring resistor. So that the display corresponds to the actual temperature, the bridge circuit and the amplifier has to be balanced.The adjusting expenditure for this is considerable. Moreover, the demands to be made on the circuit parts which work in analogue manner lead to the fact that a circuit of this kind can become expensive.

The task of the invention is to provide a method which processes digitallythetemperature- dependent resistance value of the measuring resistor.

According to the invention, there is provided a method for the digital detection of a temperature, in which the respective resistance value of a temperature-dependent measuring resistor is converted into a pulse repetition frequency and in which measuring pulses which occur during a gate pulse and which are dependent upon the pulse repetition frequency are counted and the counting result is indicated as a temperature value, characterised in that the measuring resistor lies in a frequencydetermining control circuit of, and controls the frequency of, a multivibrator, in that the measuring pulses which occur at 0 are suppressed, and in that the multivibrator is so tuned at a specific temperature different from 0" that the difference of the number of the measuring pulses occurring at this temperature and the number of the suppressed measuring pulses corresponds to the numerical value of the specific temperature. In the case of this method, the resistance value corresponding to a respective temperature is converted directly into a pulse repetition frequency. An analogue comparison or an analogue compensation is dispensed with. The measuring pulses which occur at 0 C or F are suppressed and do not arrive at the display, so that at 0 actually 0 is indicated. So that, in the case of temperatures which are different from 0, the correct number of measuring pulses occurs, the multivibrator is appropriately preset at a tuning temperature.The correct display then ensues at other temperatures. A particularly high display accuracy emerges when there is used a measuring resistor with a temperature-dependency as linear as possible and a multivibrator having the measuring resistance in a charging circuit thereof and whose period or pulse duration depends linearly upon the measuring resistance in its charging circuit.

For the detection of temperatures lying above 0 , there can be derived from the multivibrator a gate pulse having a linearly temperatu re-dependent pulse duration and the measuring pulses can be formed from counting pulses of constant frequency which occur during the duration of one of the gate pulses. For the detection of temperatures lying below 0 , the measuring pulses can be derived from counting pulses of the multivibrator which occur during the duration of gate pulses of constant frequency. The construction of a circuit arrangement for carrying out the said method is particularlysim- ple if temperatures lying either below 0 or above 0 are intended to be detected.However, it is also possible to expand the said method in such a way that temperatures lying both below 0 and above 0 can be detected.

The method can also be applied to means having a control system.

Also, according to the invention, there is provided a method for the digital detection of a temperature, in which there is used a temperature-dependent measuring resistor, and measuring pulses which occur during a gate pulse are counted and the counting result is a measure of temperature, characterised in that the measuring pulses which occur at 0 are suppressed, with there being suppressed, at temperatures different from 0 , as many measuring pulses, per gate pulse, as are equal to the number of measuring pulses suppressed, per gate pulse, at 0 , and in that a control circuit is so set that, at a specific temperature different from 0 , the difference, of the number of measuring pulses occurring, per gate pulse, at said specific temperature, and the number, of said last-mentioned measuring pulses, which are suppressed during said gate pulse, is, or is directly proportional to, the numerical value of said specific temperature.

Advantageous examples of the method and of circuit arrangements for carrying it out will become apparent from the following description.

In the accompanying drawings, which show, by way of example, several embodiments of the invention: Figure 1 shows an exemplary embodiment of a circuit arrangement for carrying out the method; Figure 2 shows a pulse diagram; Figure3 shows an enlarged partial circuitforthe detection of positive and negative temperatures; Figure 4 shows a partial circuit designed as a control system; Figure 5 shows a further exemplary embodiment; Figure 6 shows a circuit arrangement for tuning the circuit in accordance with Figures 1 or 5; and Figure 7 shows another exemplary embodiment.

Type designations of examples of integrated circuits that can be employed are indicated in the Figures. For the gates shown there can be employed, for example, those from the series MC1 ...

(Motorola).

Referring to the drawings, there is shown in Figure 1 atemperature-dependent resistor 2 and a capacitor 3 lying, at a timing generator 1, in a frequencydetermining charging circuit. The resistor 2 has a linear positive temperature coefficient. It consists, for example, of an iron-nickel alloy. Connected in advance of the measuring resistor 2 is an adjustable voltage regulator4. There thereby occurs at the output 5 of the timing generator 1 a pulse repetition frequency which is dependent upon the temperature which acts on the measuring resistor 2. The pulse repetition frequency can be preset by means of the voltage regulator 4.A relationship, linear in the measuring range of interest, between the temperature and the period of the pulse repetition frequency can be achieved by means of the RC device 2,3 in the case of know timing generator circuits.

Temperature-independent resistors in the charging circuit 2, which could lead to non-linearity, are avoided.

Connected to the output 5 is a multi-stage divider 6, connected subsequent to which is an AND gate 7.

Applied to a further input 8 of the AND gate 7 is a constant pulse repetition frequency which, for example, may be derived from the alternatingcurrent mains and amounts to 100 Hz.

Connected to the AND gate 7 is an AND gate 9, which lies at the input of a blocking register 10. The blocking register 10 is so constructed that it suppresses an adjustable number of measuring pulses present at the output of the AND gate 7. For this, preselection switches 11 and 12, shown in Figure 1, are provided. In practice, also a programmable blocking register (see Figure 6) can be used. Connected sub sequent to the blocking register 10 as well as to the preselection switches 11 and 12 is a further AND gate 13, the output of which lies, on the one hand, by way of an inverter 14, at the AND gate 9 and, on the other hand, at one input of a fourth AND gate 15.

Another input of the AND gate 15 is connected to the AND gate 7.

Connected subsequent to the AND gate 15 is a counter 16, a latch 17, a decoder 18 and a display unit 19.

The following dimensioning examples illustrate the mode of operation of the described circuit: First of all let it be assumed that the cold resistance value, at 0 , of the measuring resistor 2 stands in the ratio of 1: 2 to its warm resistance value, at 300"C.

Thus, at O"C, n pulses and, at 300 C, 2n pulses, occur in a unit of time. If it is assumed that the timing frequency of the timing generator 1 at 0 C amounts to 5.461 kHz and the divider has 14 stages, then the duration of a gate pulse present at the output of the divider 6 will amount to 16,384/5.461 kHz = 3 s. Proceeding from the frequency of the counting pulses present at the input 8 being 100 Hz, then at the output of the gate 7, at 0 C, 300 pulses will occur during one gate pulse. In order that, despite these 300 pulses, "000" will appear in the display 19, the blocking register 10 is so set that it suppresses 300 pulses.As soon as 300 pulses have run into the blocking register 10, the AND gate 9 is blocked by way of the inverter 14 and the AND gate 15 is freed.

Since, in the described instance, at 0 no further pulses follow, the display "000" is effected.

Under the described conditions, at the temperature of 300"C there will occur a timing frequency of 2.730 kHz. The duration of one gate pulse thus then amounts to 16,384/2.730 kHz = 6 s. With a counting pulse frequency of again 100 Hz there now occur at the output of the gate 7 600 measuring pulses during one gate pulse. The first 300 measuring pulses are suppressed by the blocking register 10 and thus do not pass into the counter 16. The further 300 pulses are counted in the counter 16 and lead to the display "300". Thus the display is equal to the temperature occurring at the measuring resistor 2. The same considerations apply for further temperatures.In this respect, reference is made to the Table which follows as an example: Temperature ("C) 0 150 300 450 600 Resistance (A) 100 150 200 250 300 FrequencyF(kHz) 5.4613 3.64 2.7307 2.1845 1.82 1/F (ms) 0.1831 0.2747 0.3662 0.4577 0.5494 Gate pulse (s) 3.0 4.5 6.0 7.5 9.0 Number of the counting pulses 300 450 600 750 900 Display "000" "150" "300" "450" "600" In othertemperature ranges or with other resistance values of the measuring resistor 2, taking into account the time constant of the RC device 2,3 and the divider ratio, there can similarly be achieved the resultthatthe numberofthe measuring pulses less the measuring pulses occurring at 0 corresponds to the respective temperature.The period 1/F of the timing frequency is, as a function of the respective temperature, directly proportional to the resistance course, since the period of the timing generator is determined by the time constant of the RC device.

Shown in Figure 2, in the linesa andb, is the length of one gate pulse in the case of the said ratio of cold resistance to warm resistance of 1: 2 at 0 C and 300"C. The range during which occurring measuring pulses are suppressed is hatched. Shown in the lines c and d is the same representation for a resistance ratio of 1:1.5. With this resistance ratio the number of the pulses masked out by the blocking register 10 must be set correspondingly greater. The smaller the temperature coefficient of the measuring resistor, the longer must the gate pulse be set and the higher must the blocking value of the blocking register be selected.

Similar considerations apply to the detection of negative temperatures. Here, however, the pulses present at the output of the divider 6 are to be considered as counting pulses. The frequency lying at the input 8 represents the gate pulses.

Shown in Figure 3 is a partial circuit with which positive and negative temperatures can be detected. Connected to the gate 7 are the components shown in Figure 1. The divider 6 is, in the case of the exemp lary embodiment in accordance with Figure 3, subdivided into two stages 6' and 6". Three change-over switches 20,21 and 22 are provided. By means of the change-over switch 20, the output voltage of the voltage regulator 4 and thus the timing frequency can be changed over. By means of the change-over switch 21, the output of the divider 6' can selectively be applied to the divider 6" or directly to the gate 7.

By means of the change-over switch 22 the input 8 can selectively be connected by way of the divider 6", or directly, to the gate 7 In the case of the position of the change-over switches 20, 21 and 22 which is shown in Figure 3, there is set the circuit state shown in Figure 1, which is designed in accordance with the described example for the detection of positive temperatures.

If negative temperatures are to be displayed, then the three change-over switches 20,21 and 22 are changed over. In the case of the detection of negative temperatures, one can proceed from the fact that, in connection with the above example, the blocking register suppresses, both in the case of positive and in the case of negative temperatures, the same number of measuring pulses. In connection with the example described, the divider 6' is a six-stage divider and the divider 6" is an eight-stage divider. With a timing frequency of 7.5 kHz at 0 C and the divider 6' now connected directly to the gate 7, the measuring pulses assume a length of 64/7,500 kHz = 8.53 ms. The 100 Hz pulses present at the input 8 are converted by way of the divider 6" into gate pulses with a pulse duration of 256/100 Hz = 2.56 s.It thus results that, per gate pulse, there occur, at the output of the gate 7,2.56 s/8.53 ms = 300 pulses. As already stated, the blocking register 10 suppresses these first 300 pulses, so that "000" appears in the display 19.

With a fictitious value of-300 C, theoretically in accordance with the above assumptions the timing frequency would amount to 15 kHz. The measuring pulses would thus have a pulse duration of 4.27 ms.

Per gate pulse thus 600 pulses would occur, in which respect after the suppression of the first 300 pulses still 300 pulses are available for the display. Thus the value "300" would be displayed. Corresponding considerations apply to other temperatures.

In the case of the circuit in accordance with Figure 3, the change-over switches 20,21 and 22 can be switched electronically for a cyclic interrogation. In the case of positive temperatures, then upon the interrogation, in the switching position of the change-over switches 20,21 and 22 which is associated with negative temperatures, "000" will always appear in the display. The same applies in the converse case with negative temperatures. If this "000" display is undesirable, then it can be suppressed.

In the embodiment to which Figure 4 relates, the circuit in accordance with Figure 1 is enlarged into a control system. The circuit part lying to the left of the gate 15 is not shown in Figure 4. corresponds to the circuit partto the left of the gate 15 in Figure 1. In the arrangement shown in Figure 4, connected subsequent to the latch 17 is a comparator 23 which compares the content of a desired-value transmitter 24 with the content of the latch 17 and, according to the result of the comparison, switches controlled means 25, for example a heating body, which acts on the measuring resistor 2. For the selective display of the temperature reached or of the set temperature, a change-over switch 26 is connected in advance of the decoder 18.

In the case of the exemplary embodiment in accordance with Figure 1, the timing generator 1 forms an astable multivibrator having a relatively high pulse repetition frequency, the period of which is controlled by the RC device 2,3 and is steppeddown by the divider 6. In the case of the exemplary embodiment in accordance with Figure 5, there is provided, instead of the timing generator 1 and the divider 6, a monostable multivibrator 1'. The duration of the output pulse of the multivibrator 1' is linearly dependent upon the RC device 2, 3. This means that also the period of the output pulse train of the multivibrator 1' and thus also the frequency thereof depends on the RC device 2, 3.For the triggering of the multivibrator 1', the negative flank of the gate pulse present at the output of the multivibrator 1' is evaluated by means of a capacitor 27, a resistor 28 and a diode 29. The duration of the astable state of the monostable multivibrator 1' is very short as compared with the duration of the gate pulse. The resetting of the blocking register 10 at the beginning of each gate pulse is effected similarly by way of the multivibrator 1'. An external connection 30 is provided, so that at the start of the operation a reset can be effected. The same applies in the case of the exemplary embodiment in accordance with Figure 1.

For the rest, the mode of operation of the circuit in accordance with Figure 5 is the same as described.

The circuit in accordance with Figure 5 can be enlarged, like the circuit in accordance with Figure 1, in the manner described with reference to Figures 3 and 4.

The adjusting of the described circuits can be undertaken approximately in the following manner: If the counting frequency present at the input 8, the desired temperature range, the temperature coefficient of the measuring resistor 2 and, in the case of the circuit in accordance with Figure 1, the divisor ratio of the divider 6 or 6' and 6" are fixed, then the setting of the blocking register 10 is to be undertaken in such a way that at a temperature of 0e the display "000" appears. Moreover, the timing frequency is to be so adjusted by means of the voltage regulator 4 that at a selectable tuning temperature, for example 200", the value corresponding to the numerical value of this temperature appears in the display 19. On account of the mutual dependency of the two variables that have to be adjusted, the adjustment has to be carried out in a stepwise manner.

One possibility of carrying out the adjusting is described with reference to Figure 6. A test stand has an adapter circuit 31, which in principle corresponds to the circuit in accordance with Figures 1 or 5. The components corresponding to one another are designated with the same reference numbers and the indexa. Connected into the circuit that is to be balanced is, in addition to the measuring resistor 2, a standard resistor 2', the resistance value of which corresponds to the resistance value of the measuring resistor at the temperature 0 . The measuring resistor 2 is kept at the tuning temperature of, for example, 200eC. The two resistors 2 and 2' can be switched selectively by means of a change-over switch 32.Used as blocking register 10 is a programmable blocking register, in which respect "programmable" is in this context to be understood in such a way as to indicate that the desired value is adjustable. For this, lying at the output of a counter (e.g. 4020) is a PROM (programmable store) in which for the programming in known manner electrical connections are burned through. The blocking register 10a is formed by a forwards/backwards counter, subsequent to which selector switches 1 1a and 1 2a are connected.

If, initially, the change-over switch 32 is switched to the measuring resistor 2 held at tuning temperature, then the timing frequency is so set by means of the voltage regulator 4 that there appears at the display 19a the numerical value of the tuning temperature, for example 200"C. If, now, the change-over switch 32 is changed over to the resistor 2', then the value "000" is intended to appear at the display 19a.

If this is not the case, the selector switches 1 1a and 12a are appropriately adjusted. Then a change-over to the measuring resistor 2 again is effected and the possibly necessary renewed adjustment of the timing frequency is undertaken. These procedures are repeated until in actual fact, upon the connection of the resistor 2', the value "0", and upon the switching of the resistor 2' the value "200", appear in the dis play 19a.

Then, at the voltage regulator 4, the timing frequency is correctly set and in the blocking register 1 or the number of pulses to be suppressed is fixed.

The change-over from the measuring resistor 2 to the resistor 2' can also be effected electronically by way of a multiplex control. Then at a respective display there are displayed practically simultaneously the display values at 05C and of the tuning temperature, if necessary 200eC. Thus the expenditure of time necessary for the balancing becomes very small.

After the timing frequency has been set at the voltage regulator and the number of the pulses to be suppressed has been fixed in the blocking register 10a, the result stored in the blocking register 10a is to be transferred to the blocking register 10. For this, initially the blocking register 10 is reset at the input 30. Then so many pulses are counted into the divider 6 that the output thereof lying at the gate 7 is safely H. Then the blocking register 1 Oa is counted back by means of a timing generator 33.For this, the timing generator 33 is connected by way of an AND gate 34 and an OR gate 35, to which moreover the AND gate 9a is connected, to the blocking register lOs. The switching-on of the timing generator and the changeover of the blocking register 10a to "counting backwards" is effected by closing a switch 36. With the switch 36 closed, then, by way of an inverter 37, the gate 7a is blocked and the gate 34 freed. The backwards-countingtiming pulses of the timing generator 33 are counted by way of the gate 34, the input 8 and the gates 7, 9 into the blocking register 10. As soon as the blocking register 1 Oa has been counted back to zero, the gate 34 is blocked by way of an inverter 38.Thus, in the end-result, the value set beforehand in the blocking register 1 Oa stands in the blocking register 10. Finally, this value is to be stored in the blocking register 10 by means of a programming command to be applied at one input 39 of the blocking register 10.

Shown in Figure 7 is a further exemplary embodiment of the invention. In this case, instead of the described blocking register 10, a monostable multivibrator 10' is provided. At the output of the multivibrator 10' there lies an inverter40, which is connected to the one input of the AND gate 15. The pulse duration of the multivibrator 10' can be adjusted by means of an adjustable resistor 41, a capacitor42 being coupled up to the multivibrator.

During the duration of the pulse, the AND gate 15 blocks and thus does not allow any measuring pulses which occur at the output of the gate 7 during the duration of a gate pulse to pass into the counter 16.

The pulse duration of the multivibrator 10' is so selected by means of the adjustable resistor 41 that at 0" none of the measuring pulses goes by way of the AND gate 15. The triggering of the monostable multivibrator 10' can be effected with the negative flank of the gate pulse occurring at the output of the divider 6. With the negative flank also the divider 6 can be reset, after which the next gate pulse begins.

In this respect, the resetting of the divider 6 should be effected with a certain delay, so that the multivibrator 10' is reliably triggered. The circuit in accordance with Figure 7 can be enlarged in the manner described in the case of Figures 3 and 4.

Numerous further exemplary embodiments lie within the scope of the invention. Thus, it is, for example, possible to use the monostable multivibrator in accordance with Figure 7 also in the case of the circuit in accordance with Figure 5. Instead of the counting pulses at the input 8 being derived from the mains frequency, a constant-frequency oscillator can be used. If non-linear temperature-dependent resistors are used, a linearisation can be undertaken by connecting an appropriately programmed read storey (ROM) subsequent to the gate 7. The described circuit can also be so constructed that, selectively, temperatures in accordance with the Celsius scale and in accordance with the Fahrenheit scale can be displayed. This can be effected by an appropriate change-over possibility in the timing generator or at the divider.

Claims

1. A method for the digital detection of atemper- ature, in which the respective resistance value of a temperature-dependent measuring resistor is converted into a pulse repetition frequency and in which measuring pulses which occur during a gate pulse and which are dependent upon the pulse repetition frequency are counted and the counting result is indicated as a temperature value, characterised in that the measuring resistor lies in a frequency determining control circuit of, and controls the frequency of, a multivibrator, in that the measuring pulses which occur at 0" are suppressed, and in that the multivibrator is so tuned at a specific temperature different from 0" that the difference of the number of the measuring pulses occurring at this temperature and the number of the suppressed measuring pulses corresponds to the numerical value of the specific temperature.

2. A method for the digital detection of a temperature, in which there is used a temperaturedependent measuring resistor, and measuring pulses which occur during a gate pulse are counted and the counting result is a measure of temperature, characterised in that the measuring pulses which occur at 0" are suppressed, with there being suppressed, at temperatures different from 0 , as many measuring pulses, per gate pulse, as are equal to the number of measuring pulses suppressed, per gate pulse, at 0 , and in that a control circuit is so set that, at a specific temperature different from 0 , the difference, of the number of measuring pulses occurring, per gate pulse, at said specific temperature, and the number, of said last-mentioned measuring pulses, which are suppressed during said gate pulse, is, or is directly proportional to, the numerical value of said specific temperature.

3. A method as claimed in Claim 1, characterised in that for the detection of temperatures lying above 0" gate pulses having a linearly temperature- dependent pulse duration are derived from the multivibrator and in that the measuring pulses are formed from counting pulses of constant frequency which occur during the duration of the gate pulses.

4. A method as claimed in Claim 1 or 3, characterised in that for the detection of temperatures lying below 0" the measuring pulses are derived from counting pulses of the multivibrator which occur during the duration of gate pulses of constant frequency.

5. A method as claimed in Claim 4 insofar as dependent upon Claim 3, characterised in that for the detection of temperatures lying below and above 0 , a timing frequency, a divisor ratio of the pulses derived from the multivibrator and a divisor ratio of the pulses of constant frequency are cyclically changed over.

6. A method as claimed in any one of Claims 1 and 3 to5, characterised in that, for the control of a control system, the respective counting result is compared with a desired value.

7. A circuit arrangement for carrying out the method claimed in claim 1, characterised in that the measuring resistor has a linearly-extending temperature coefficient and forms, with a capacitor, an RC device, upon the time constant of which there depends linearly the period or pulse duration of the multivibrator.

8. A circuit arrangement as claimed in Claim 7, characterised in that the multivibrator is formed by a timing generator, subsequent to which a multi-stage divider is connected.

9. A circuit arrangement as claimed in Claim 8, characterised in that the multi-stage divider produces gate pulses at a temperature lying above 0 , and in that the number of the divider stages is so dimensioned that the number of the counting pulses which occur during a gate pulse is greater than the numerical value ofthetemperature lying above 0 .

10. A circuit arrangement as claimed in Claim 8, characterised in that the multi-stage divider produces, at a temperature lying below 0 , counting pulses, whose number occurring during a gate pulse is greater than the numeral value of the temperature lying below 0 .

11. A circuit arrangement as claimed in Claim 7, characterised in that the multivibrator is a monostable multivibrator.

12. A circuit arrangement as claimed in Claim 11, characterised in that the monostable multivibrator produces, at a temperature lying above 0 , gate pulses whose duration is so pre-set, by means of an adjustable current or voltage regulator, that the number of the counting pulses occurring during a gate pulse is greater than the numerical value of the temperature lying above 0 .

13. A circuit arrangement as claimed in Claim 11 or 12, characterised in that the monostable multivibrator produces, at a temperature lying below 0 , counting pulses whose number occurring during a gate pulse is greater than the numerical value of the temperature lying below 0 .

14. A circuit arrangement as claimed in any one of the preceding claims 8 to 10, characterised in that tuning of the pulse repetition frequency of the timing generator is effected by means of an adjustable current or voltage regulator which is connected in advance of the measuring resistor.

15. A circuit arrangement as claimed in any one of preceding claims 7 to 14, characterised in that provided for the suppression of measuring pulses is a programmable blocking register which at all temperatures filters out as many measuring pulses as occur at 0'.

16. A circuit arrangement as claimed in any one of the preceding Claims 7 to 14, characterised in that provided for the suppression of measuring pulses is a monostable multivibrator in which respect the measuring pulses which occur during the pulse duration thereof are blocked and the pulse duration is so set that at all temperatures as many measuring pulses are suppressed as occur at 00.

17. A method for the digital detection of a temperature, substantially as herein described with reference to Figures 1 and 2, or Figure 3, or Figure 4, or Figure 5, or Figure 7 of the accompanying drawings.

18. A circuit arrangement for the digital detection of a temperature, substantially as herein described with reference to Figures 1 and 2, or Figure 3, or Figure 4, or Figure 5, or Figure 7, of the accompanying drawings.

19. A method of adjusting a circuit arrangement for the digital detection of a temperature, substantially as herein described with reference to Figure 6 of the accompanying drawings.