NO852125L - PROCEDURE AND APPARATUS FOR CODING AND SYNCHRONIZING DATA IN PULMETRY METHOD - Google Patents

Description

The present invention relates to the method and equipment

for coding and synchronizing data in pulse telemetry systems. The invention is particularly suitable for use when processing data obtained at the bottom of a drilling

hole while the hole is being drilled.

Data acquired at the bottom of a borehole while the hole is

during drilling can be sent to the surface for treatment using pressure signals or acoustic signals that are propagated through the drilling fluid. US Patent Nos. 2,924,432, 3,789,355, 3,949,354, 3,964,556 and 3,983,948 disclose various arrangements for transmitting such data to the surface through the drilling fluid. Usually this data is coded and sent in the form of positive or negative pressure pulses through the drilling fluid.

However, noise signals produced by the drilling equipment and the drilling process tend to overshadow some of the data pulses in the previously known coding arrangements, and when a part of the data pulses is lost it is difficult to determine the particular parameters being measured, due to the normal variation in the pulse transmission sequence.

In addition, with the previously known code arrangements, considerable time is required to initiate the ongoing measurement process in the borehole after a drilling stop.

The above-mentioned difficulties are overcome according to the present invention by using a pulse code where the time intervals between successive pulses in a pulse series represent the size of the relevant data parameters and allow the measurement of these parameters, as well as by allowing extra pulses with a predetermined time location to be included in the series of coded data pulses, thereby increasing the sewing machine's ability to highlight or distinguish data pulses from noise signals. The pattern of extra pulses in relation to the data pulses is such that there is a low probability that they can be produced by random noise. In addition, synchronization pulses are used at the beginning of each predefined unit of data information, thereby allowing identification of the special parameters sent telemetrically to the surface, even if one or more of the pulse code signals that provide a parameter measure are masked by noise.

The order in which the pulse code signals are produced is continuously monitored to make it possible to start telemetry systems quickly after a drilling stop at the place in the data line where it would have been if the drilling stop had not taken place.

The encoding, synchronization and sequencing can be achieved by programming a microprocessor or by means of hardware.

The invention will now be described in more detail with reference to the attached drawings, on which: Fig. 1 shows a pulse code form that utilizes extra pulses. Figures 2-4 show alternative pulse codes with extra pulses. Fig. 5 shows three types of identification patterns that can be included in the pulse codes. Fig. 6 shows how the pulse code signals can be generated by circuit hardware and used to generate negative pressure pulses in the drilling fluid. Fig. 7 and 8 show how analogue parameters can be transformed into binary signals under control from a microprocessor, thereby producing the pulse codes. Fig. 9 shows how a synchronized new start-up can be included in the code plan, so that the system can be started quickly after a drilling stop at that place in the data line

where it would have been if the punch had not

found place.

Fig. 10 shows how the pressure pulse signals can be computer-processed on the surface to produce a reading of

the parameters measured downhole.

A pulse can be defined as a predetermined sequence of state changes (eg pressure, voltage) within a fixed time period. In practice, a pulse can be a pressure drop followed by a return (increase) to normal pressure, normal pressure being the pressure in the circulation system for drilling fluid without a pulse. Negative pressure pulses are preferable, but the coding scheme is equally applicable to positive pressure pulses.

In the embodiments shown here, the duration of a pulse is regarded as a pressure drop for a fixed time period (eg 1 second or 0.5 second) followed by 1 second of normal pressure.

The measurement of the various parameters in the borehole, like this

such as gamma radiation, propagation resistance, magnetic field, temperature etc. are available in analogue form. The time intervals between successive data pulses in a pulse train indicate

the analog measured value for the respective parameters.

A "frame" is defined as the period of time required to transmit a complete set of data. In order to maintain synchronization within the frame, the relevant data is arranged in "sub-frames". • Each sub-frame is a "synchronization interval1" long, and the starting position is marked by a synchronization pulse.

Table 1 shows a form that uses 15 sub-frames.

Two "data words" are transmitted during each sub-frame except

from the sub-frame 15 where a data word is transmitted along with a sample pattern and "frame identification" pulses.

A data word is defined to be the equivalent of an eight-bit binary number (that is, an integer in the range 0 - 255)- The frame identification (or "frame synchronization") pulses make it possible to identify the first subframe, thus allowing a pulse detector/decoder on the surface to identify the order of the data transfer.

Table 2 shows a scheme that utilizes 11 subframes and three data words in each subframe.

Sample pattern

1 Available space for sample pattern Frame ID pattern

When the last subframe is completed, the transmission resumes at subframe 1 without any delay, the sync pulse for subframe 1 being one synchronization interval after the sync pulse for the last subframe (subframe 15 in Table 1).

After synchronization is achieved (the synchronization pulses are recognized as the only pulses that do not vary over a synchronization interval, and the subframe numbers can be decoded after the frame identification pulses are recognized), the surface detector or decoder can assume (interpolate) the time location of the subsequent synchronization - and identification pulses and only the data pulses need to be detected to achieve correct decoding of all data. The synchronization is also maintained during periods when no data pulses are transmitted, and it is then possible to restart the decoding of the daa immediately after an established connection without any delay whatsoever to restore the synchronization.

In practice, the detector or decoder on the surface continuously tries to search for synchronizing and identification pulses for adaptation to each small operation in the time-determining clocks both in the equipment down the hole and on the surface.

A subframe is defined as a time period of duration a synchronization interval which is preceded by a synchronization pulse. To transfer two data words per synchronization interval, two additional pulses are required. The time from the end of the synchronization pulse to the first data pulse is proportional to the data word (No. 1) that is transmitted.

Time 1 = Data 1 dT,

where DT = Time for a unit of transmission data Data 1 = Number of transfer units

(data value in the range 0 - 255)

Similarly, the time from the end of the first to the second data pulse is proportional to the second data word (no. 2).

The necessary information to be able to distinguish between data pulses and noise pulses is obtained by producing a

pattern of pulses that is unlikely to be achieved by random noise. This requires additional pulses to create said pattern.

Fig. 1 shows a pulse kernel which is suitable for transmitting the data indicated in table 1. Each subframe has two data words, and the analog measure for the data parameters includes the time between the synchronization pulse and Dl as well as the time between Dl

and D2.

An "extra pulse" R is produced midway between adjacent pairs of data pulses. This is used to distinguish between time data pulses and noise pulses. Any two data pulses can thus only be regarded as data pulses (D1 and D2) if a further pulse (R) occurs midway between the data pulses.

The timetable in fig.l can be as follows:

The duration of a pulse is 2 seconds. (A pressure drop of

1 second followed by 1 second of normal pressure).

(The synchronization interval could have been chosen equal to 55.8 seconds. However, sixty seconds was chosen as an appropriate time interval for testing.)

Although the coding scheme processes the equivalent of 8-bit (binary) numbers, this system does not limit the transfer of two "information sections" per subframe. When the analog number is decoded at the surface, it is very easy using a digital calculator to recover the 8 binary bits of information sent out by the downhole tool.

We thus transmit essentially 16 independent pieces of information in each subframe (2 8-bit words).

This basic term is used when transmitting pressure information in subframes 8/9 and 13/14 in table 1. The sensors down in the boreholes are measured using a 12-rbit ADC. Although the additional accuracy that can be obtained by using a 12-bit number (1/4096 compared to 1/256 for an 8-bit number) is not necessary for all sensors, it is actually necessary to determine the borehole pressure (several thousand psi) with an accuracy of a few psi. The measured 12-bit number is then transmitted as two 8-bit numbers with a 4-bit overlap, as shown below.

All transmitted mud pulse data is represented (downhole) as 8-bit binary numbers.

"Press 1" is the most significant 8 bits in the present 12-bit raw data, while "press 2" is the least significant 8 bits in this 12-bit raw data. Since data words are transmitted using an analog scheme, the probability of correct decoding of the individual data bits is greatest for the most significant bits. 1 seconds], a small error will be introduced, as for example the number 211 can be decoded as 212).

Fig. 2 shows a pulse pattern which is suitable for the transmission of the specified data in table 2.

The duration of a pulse is reduced to half a second of pressure drop followed by 1 second of normal pressure. The time for a data unit (dT) has been reduced to 1/16 second. Instead of reducing the synchronization interval, a third (8-bit) data word is transferred in the time interval that follows the second data word. A further extra pulse is then required between the second and third data pulse, to ensure identification of said third data pulse.

Fig. 3 shows a pulse pattern similar to that in fig. 2, namely with extra pulses RI midway in time between the following data pulses D1 and D2, but with extra pulses R2 not midway in time between the following data pulses D2 and D3. The pulses.R2.-can instead be placed in any desired time relationship between the subsequent data pulses. Such a code kernel is asymmetric in time and is advantageous when several "groups of three" pulses (two data pulses + one additional pulse) occur within a sub-frame. If desired, both extra pulses RI and R2 can be asymmetric in time with respect to the adjacent data pulses.

Although the code scheme in fig. 2 is selected to fit

three data words in full scale per subframe, the data in question is normally not at full scale and there is therefore "unused" time at the end of most subframes, during which additional data can be transferred. The code form can be set up for the transfer of additional data if time is available for this. This will change the data rate from the current fixed rate of three 8-bit words per minute to an average data rate that will not be less than the current rate.

Although the code scheme in fig. 2 requires two pulses (e.g.

R2 and D3) for the addition of a data word, it is possible to apply an extra pulse after each data pulse or in between each pair of data pulses and maintain control of all data.

Fig. 4 shows such a code core which increases the total number transmitted within a subframe by using an extra pulse between each pair of data pulses.

The maximum data rate is limited by the pulse width. The following example should be considered.

A maximum number of 40 pulses can then be transmitted.

At three pulses per pairs of data words, this can be interpreted as 13 pairs of data words (with a 0 value), namely 26 data words per minute.

Another example concerns average data values. For 8-bit data words, the full-scale data value is 255, and the mean value is therefore 127.5. At 1/16 seconds per data unit, this corresponds to 8 seconds per computer word.

Although a tool down the borehole cannot be expected

to produce random data, most sensors (for gamma radiation and formation resistance) are set so that normal sensor readings lie roughly in the middle of the sensor's working area, in order to thereby be able to record both unusually high measurement values and unusually low values.

The sort of data that is derived will thus tend to be approximately average value data for "typical" formations.

As indicated in fig. 5, the data frame structure can be extended to include different data types. Three different frames can be transmitted, namely normal frames, directional frames and sample pattern frames. Each frame comprises a predetermined number of subframes. The frame identification pattern is transmitted at the end of the first subframe in each frame.

In the case of the pulse coding scheme in fig. 2, only two data words will be included in the subframe when a frame identification pattern is transmitted, thereby ensuring that no overlap occurs between said pattern and the third data pulse. A portion of the frame identification pattern is transmitted during the period between the complete data time of 56.8 seconds and the end of the subframe. This contributes to the identification of the frame pattern, as data pulses are never transmitted during this time period.

The programming schemes in Figures 1-5 can be produced by programming a suitable microprocessor, such as e.g. RCA 1802, or using hardware circuits.

Fig. 6 illustrates a method for producing code schemes using hardware in the form of electrical circuits. The embodiment shown applies to the pulse pattern in fig. 2, but it will be obvious that the circuit in question can be modified to produce any of the pulse patterns discussed above. Measurement of only three data parameters for a subframe is shown for simplicity. However, it will be obvious that additional data parameters can be measured in the system at the selected number of subframes.

Data to be transferred to the surface is measured in analogue form, such as e.g. voltage, using the sensors 20, 22 and 24. The voltage values produced by the sensors

22 and 24 are divided by means of division units 26, 28, 30 and 32 to be used in the formation of the extra pulses RI

and R2. The voltages thus produced are sensed by a step switch 34 which is driven by a coil 36. A terminal 38 on the switch is grounded and represents the time value 0 in each subframe. A terminal 40 of the switch is connected to a battery 42 which produces the synchronization pulses.

The rotor in the tap changer 34 is connected to a resistor/capacitor network 44,46, which in turn is connected to a trigger circuit 48. The time constant of the resistor/capacitor network 44, 46 causes the trigger to generate pulses of 0.5 second duration at time points that represent the voltages emitted from the respective sensors. The time interval between the data pulses emitted on the output side of the trigger 48 thus constitutes an analog representation of the size of the

data measured by sensors 20, 22 and 24.

If the extra pulses RI and R2 are to be equally distributed in time between the adjacent data pulses, the division unit 26, 28, 30 and 32 divides the voltages produced by the sensors 22 and 24 by 2.

The rotor in tap changer 34 is located at terminal 38 at time 0. After starting, the rotor moves to terminal 40 which is impressed with a voltage which immediately affects outlet 48 to produce a synchronizing pulse. After further impact, the rotor scans terminal 50 and the trigger 48 then produces a data pulse Dl, Then the rotor comes into contact with terminal 52, and the trigger 48 then emits an extra pulse 1*1, Then it comes into contact with terminal 54 to trigger a data pulse D2. The extra pulse R2 and the data pulse D2 are produced when the rotor The coil 36 of the tap changer is first energized by a pulse produced by the oscillator 60 and the pulse generator 62, which emits a pulse every sixtieth of a second and which is transmitted through an amplifier 64 to the coil 36. During a synchronization interval the coil is energized 36 then in steps of the pulses produced by the trigger 48.

A counter 66 is connected to the oscillator 60 and the pulse generator 62. It serves to activate the generator 68 for the data frame identification pattern, the generator 70 for the direction frame identification pattern, as well as the generator 72 for the sample frame identification pattern at the time points mentioned frames are to be entered in the pulse pattern in table 2.

The data pulses and extra pulses as well as the frame identification patterns are transmitted through an amplifier 73 to a valve 74 to cause this to open to produce negative pressure pulses in the drilling fluid in response to each of the pulses.

Different types of valves 74 can be used. A suitable valve 74 is disclosed in US Patent Application No. 06/190636 filed September 25, 1980. A suitable control circuit for actuating such a valve is disclosed in US Patent Application No. 06/139767 filed 7. December 1981.

A valve for generating positive pulses is disclosed in US Patent Application No. 355,991, filed March 8, 1982.

Figures 7 and 8 show here how the analogue pulses can be generated under control from a microprocessor, such as e.g. RCA 1802.

The order of transfer of the different frame types can be varied and determined in the microprocessor that works in the tool down in the borehole. This sequence will best be shown in a flow chart:

Fig. 7 is a simplified block core which indicates how the pulses are timed in accordance with the code scheme in fig. 2. Three data words are transmitted within a synchronization interval. The synchronization interval is 60 sec-

under .

When the tool restarts, it measures data for 59 seconds.

In the following second, the three data words (8-bit

number= whole number in the range 0 -r 255). and the heart rate table is drawn up for the following minute.

The pulse table is a shift register 7.6 ■ (length 960 bits) which is clocked out at a rate of 16 bits per second. It then takes exactly one synchronization interval (60 seconds) to

clock out all data.

Data from the shift register 76 controls the pulse generating valve 74. When a "one" value is present on the output side of the shift register, the pulse valve 74 will remain open and a pulse will be transmitted.

During the first minute of the tool's working function

after a fresh start there is no data to transfer. After this first minute, however, data is transferred (clocked

out of the shift register) at the same time as new data is measured.

The sequence of setting up the pulse table includes setting a string of "one" values in the pulse table shift register 76 for transmitting a pulse, as well as "0" values to mark the time between the pulses, as indicated in fig. . 8. When the bit in question is clocked out of the shift register 1 at the aforementioned rate of 16 per second, a sequence of eight one values is required to produce a pulse of half a second.

As no extra pulse occurs between the synchronization pulse and the first data pulse, the number of 0 values required for data 1 is equal to the relevant data value (0-255). The remaining two data words are divided into two halves by the extra pulses. In the case of data 2, the number of 0 values corresponding to the first half (data 2)/ 2 is rounded down to the nearest whole value, and is set before the first extra pulse. The second half (data 2 + l)/2, rounded down to the nearest whole number, is set after the extra pulse and before the second data pulse.

An extra "+1" is required in the second sea part, then et

odd numbers not exactly divisible by two. Two examples should be considered:

Transfer data = 122,

(Data)/2 - 61.0, (data+l)/2 = 61.5 rounded to 61 Decoded data = 61 + 61 = 122

Transferred data = 123

(Data)2 = 61.5 rounded to 61.5,

(Data+l)/2 = 62

Decoded data = 61+62 = 123

A similar process is used for setting data 3.

Fig. 9 shows the changes that are required in the form to ensure that data is initiated in synchronism with the data that was transferred before the restart.: Two pieces of hardware are required to ensure synchronized restart. The first is a battery with a clock. This will allow the tool to "wait" until a new sync interval is initiated (once per minute, whenever the second reading is 0) before restarting the measurement/transmit sequence. The other is a battery with a memory register. Each time new pulse data is entered into the pulse table's shift register, the time and sequence number (subframe number) are stored in the aforementioned battery with memory register. If the tool is disconnected and restarted, this data is saved and can be inspected. Thus, the tool can be restarted at the point in its predetermined sequence where it would have been if it had not been disconnected.

The predetermined sequence (or frame) determines which data is to be measured and transmitted, as different sensors can be read every minute (every synchronization interval).

The surface equipment (decoding) always assumes that the tool in the borehole transmits its data in the order determined by the predetermined sequence and therefore does not need to be re-synchronized with the drilling tool each time it is started after stopping (each connection).

Fig. 10 shows an arrangement for processing the coded data on the surface.

The drilling rig comprises the usual rotary table 90, kelly 92, pivot pin 94, traveling block 95, mud pumps 96, mud pit 98, as well as a drill string composed of drill pipe sections 100 which are attached to the lower end of said kelly 92, as well as at the upper end of a drill collar 102 and which ends in the drill bit 104.

The pulse encoder and the valve 74 for producing negative pressure pulses can be placed in the drill collar 106 on the upper side of the drill bit 104.

A pressure transducer 108 is connected to the flow channel for the drilling fluid and this then senses the negative pressure pulses that are produced down the hole.

The sludge pumps 96 produce noise signals with certain characteristic properties. A strobe generator 110 produces strobe signals for each cycle of each slurry pump.

The signals from the pressure converter 108 and the strobe generator 110 are applied to an input module 112, where the average value of the pressure signals is derived pair by pair and the average value is stored 50 times per second in a buffer until it is required by the filter module 114.

The filter module 114 serves to remove or reduce the noise signals produced by the mud pumps 96. Different types of such filters are known within the present field. Here, however, a filter of the type shown in a simultaneously filed patent application is preferably used.

The output from the filter 114 is applied to a detector 116 which uses a suitable filter to increase the possibilities of detecting the coded pulses.

The pulse signature used in the custom filter

is a first-order approximation to a rectangular pulse that has been high-pass filtered at a frequency corresponding to l/(4'pulse width) Hz. Application of a high-pass filter makes it possible to use a simple level detector for pulse identification.

A high-speed FFT holding technique is used to implement the matched filter's convolution. In operation, the folding is performed approximately once every 20 seconds each time data is available from the filter module 114. The output signal from the adapted filters is stored in a "detection buffer" which can hold data for more than one complete subframe. (Since the normal subframe has a duration of 60 seconds, said buffer is set to hold data for an interval of 64 seconds).

A simple level-detection scheme is performed at the (overlapping) 64-second intervals. (Detection level

is a user-controlled parameter). Pulse position (time) is indicated at pulse minimum, as pulse height and width are also determined. The decoded pulses are stored in a "pulse table" for use by the decoder module 118. If the pulse width does not fit within

above certain limits, the pulse in question is considered "noise" and discarded.

Synchronization pulses for the subframe are found by searching for non-varying pulses with period time of 1 minute over the last three minutes. When such pulses are found, the detection buffer is shifted in time to ensure that the initiation of the relevant subframe will take place at: the start of the buffer. The time of the synchronization pulse is recorded for use by the decoder module 118.

Since three minutes are required for the identification of synchronization pulses, a search for frame identification pulses will be initiated within the detector module 116 before the subframe synchronization pulses are identified the first time a tool is started downhole.

This allows the device to synchronize on the first subframe sent up the hole.

Claims (23)

1. Apparatus for data coding in a pulse telemetry system comprising equipment for generating a pulse train of coded data pulses, characterized in that the time intervals between successive data pulses represent the size of the relevant data parameters, and equipment is arranged to produce extra pulses with a predetermined time location in the aforementioned series of coded data pulses, so that the ability of the telemetry system to extract or separate data pulses from noise signals increases due to of the fixed time .ratio between the extra pulses and the coded data pulses. 2. Apparatus as stated in claim 1, characterized in that each extra pulse is produced between pairs of successive data pulses and in a pre-determined period of time f hold-with rips off the pulses in said pair. 3. Apparatus as set forth in claim 1, characterized in that each extra pulse is produced at a point in time that is midway between successive pulses in pairs of data pulses. 4. Apparatus as specified in claim 1, characterized in that each extra pulse is generated between the pulses in every other pair of data pulses. 5. Apparatus as stated in claim 1, characterized in that the extra pulses are produced after every second data pulse. 6. Apparatus as stated in claim 1, characterized in that it comprises equipment for producing synchronization pulses in predetermined time ratios with said series of coded data pulses. 7. Apparatus as stated in claim 1, characterized in that successive synchronization pulses are separated from each other at fixed time intervals. 8. Apparatus for producing coded data in a pulse telemetry system comprising equipment for producing frames of pulse coded data with a predetermined number of synchronization intervals of equal duration and determined by synchronization pulses at the beginning of each synchronization interval, characterized in that the pulse-coded data is arranged in data words that represent the size of the data parameters in question, the device further comprising equipment for generating extra pulses in predetermined data words and with a predetermined time location in relation to the pulses in the data word in question in order to increase the device's ability to distinguish data pulses from noise, as well as equipment to .fr embring at least -et* .ide n-t in fission pattern of pulses at a predetermined location in each frame, the pulses in each such pattern being separated from each other by prior: specific time intervals. 9. Procedure for borehole measurement by telemetry of information using pressure pulses in the drilling fluid from the interior of the hole to the surface, characterized in that coded data pulses are generated where the time intervals between the pulses represent the size of the measured data in the borehole, while extra pulses are generated at predetermined time points in relation to the data pulses, and pressure pulses in the drilling fluid are created in accordance with both the data pulses and the extra pulses. 10. Method as stated in claim 9, characterized in that each extra pulse is produced between the pulses in predetermined pairs of data pulses and in a predetermined time ratio in relation to the data pulses in said pair. 11. Method as stated in claim 9, characterized in that synchronizing pulses are further produced which determine synchronization intervals with a predetermined time ratio to the coded data pulses. 12. Method as stated in claim 11, characterized in that subsequent synchronization intervals are counted and stored while they are produced, while the formation of pressure pulses in the drilling fluid is delayed for a predetermined period of time, so that the last stored synchronization interval remains stored when the well measurement is terminated and identifies the synchronization interval where the well measurement shall be resumed. 13. Method for borehole measurement by producing coded data representing data parameters measured in the borehole while the drilling is taking place, characterized in that a series of synchronization pulses are produced at a time interval from each other on a synchronization interval of predetermined duration, coded data pulses are produced during each synchronization interval in such a way that the time intervals between the subsequent data pulses represent the size of the measured data parameters in the borehole, while extra pulses are formed with a predetermined time ratio to the data pulses in order to thereby increase the possibilities of separating data pulses from noise signals. 14. Method as stated in claim 13, characterized in that identification patterns of pulses are created in pre-selected synchronization intervals. 15. Method for generating coded data in a pulse telemetry system where a series of synchronization pulses are created with successive pulses spaced apart in a synchronization interval of predetermined duration while coded data pulses representing data words are generated during each synchronization interval, the size of the relevant data parameters in each data word determined by the time interval between successive pulses, and said data words are generated in focused sequence in subframes of data, and a selected number of subframes are sequentially grouped into frames, each representing a complete data set. 16. Method as stated in claim 15, characterized in that each subframe is given a selected number of data words. 17. Method as set forth in claim 15, characterized in that identification patterns of pulses within previously selected synchronization intervals are also produced. 18. Procedure for borehole measurement by producing coded data representing data parameters measured in the borehole while drilling is carried out, characterized in that a series of synchronization pulses are generated where successive pulses are separated from each other by a synchronization interval of predetermined duration, coded data pulses representing data words are generated during each synchronization interval, said data words being formed in identified subframes of data in a predetermined number sequence, and a predetermined number of subframes are grouped in sequence to form frames, where each frame represents a complete data set and each data word is placed in a predetermined identifiable location in each frame, as well as the identification of the sub-frames;: are stored in sequence and the sub-frames of data pulses are applied to a pulse generator in order to thereby produce pressure pulses for transmission to the surface of the borehole after a predetermined time delay, so that when the borehole measurement is interrupted the last stored sub-frame identification will remain, stored and identify the subframe number by which the borehole measurement is to be resumed. 19. Method as stated in claim 18, characterized in that two data words are produced within each synchronization interval. 20. Method as stated in claim 18, characterized in that at least three data words are produced within each synchronization interval. 21. Method as stated in claim 18, characterized in that further extra pulses are produced in pre-selected data words within each sub-frame, in such a way that the extra pulses for a predetermined time relationship to the relevant data pulses thereby increase the possibilities for separating the data pulses from noise signals, by virtue of the present fixed time relationship between the extra pulses and the coded data pulses. 22. Method as stated in claim 18, characterized in that at least one identification pattern of pulses is produced at a predetermined location within each frame, and such that the pulses in each such pattern are mutually separated by predetermined time intervals. 23. Method for borehole measurement by telemetering information by means of pressure pulses in drilling fluid from the interior of the borehole to the surface, characterized in that a series of synchronization pulses are produced, where successive pulses have a mutual time distance of a synchronization interval of predetermined duration in order thereby to determine subframes of information while data words are generated in predetermined sequences during each synchronization interval and in the form of data pulses where the time between the predetermined pulses represents the magnitude of data parameters measured from the borehole, while certain predetermined data words form identification patterns of pulses with the pulses in each such pattern mutually separated with predetermined time intervals, and extra pulses in a predetermined time ratio to predetermined data pulses in order to thereby increase the possibilities of distinguishing data pulses from noise signals, as a predetermined number of subframes are combined in order to form frames, which is represents a complete data set and the subframes' number and storage time are stored in sequence to produce pressure pulses after a predetermined time delay in accordance with the mutually consecutive subframes of data pulses, in such a way that the last stored subframe number remains stored and can be identified as the second subframe number by which the borehole measurement shall is restarted after a stop.