JP3800498B2 - Pulse frequency signal output method and apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a pulse frequency signal output method and apparatus, and in particular, to transmit a signal measured by a measuring device such as a Coriolis mass flow meter, a pulse frequency signal output that converts the value of the measurement signal into a pulse frequency and outputs the pulse signal. The present invention relates to a method and an apparatus.
[0002]
[Prior art]
The operation of a conventional general Coriolis mass flow meter (see, for example, Japanese Patent No. 2647201) will be described with reference to FIG. As is well known, a Coriolis mass flowmeter supports both ends of a flow tube through which a fluid to be measured flows, and when the flow tube is vibrated in a direction perpendicular to the flow direction of the flow tube around the support point, This is a mass flow meter utilizing the fact that the Coriolis force acting on is proportional to the mass flow rate. The Coriolis mass flowmeter main body 1 shown in the figure is usually provided with one or two curved or straight flow tubes, a drive device for driving the flow tube, and left and right sides of the attachment position of the drive device. It has at least a left sensor and a right sensor installed at symmetrical positions.
[0003]
The flow meter electronics 10 supplies a drive signal to the drive device of the Coriolis mass flow meter main body 1 and inputs signals from the left sensor and the right sensor of the Coriolis mass flow meter main body 1 so as to be proportional to the Coriolis force. Detect phase difference. The flowmeter electronics 10 usually has a microprocessor and calculates a mass flow value based on the detected phase difference. The calculated mass flow value is output in analog form and in digital form.
[0004]
Further, the mass flow value as the measurement value is output as a pulse signal obtained by converting the measurement value into the number of pulses per pulse (pulse frequency) in order to be coupled to the downstream apparatus. The downstream device that has received the pulse signal can obtain the instantaneous mass flow value by counting the number of pulses per unit time of the pulse, and obtain the total mass flow rate by integrating the number of pulses. be able to.
[0005]
FIG. 3 is a diagram for explaining the operation of a conventional pulse frequency signal output unit that converts a measured value (flow rate value) into a pulse frequency signal using a microprocessor. This pulse frequency signal output unit is provided in the flowmeter electronics 10 shown in FIG.
[0006]
In the pulse frequency signal output unit shown in FIG. 3 (A), first, the flow rate calculation unit 12 calculates, for example, the flow rate as a measurement value at a constant cycle (sampling cycle) T. The calculated flow rate value is converted into a pulse number nt to be output by the pulse number calculation unit 13. Next, one type of pulse period a × Tw or (a + 1) × Tw is calculated by the one type of pulse period calculation unit 14 as outputting the calculated number of pulses nt during a fixed period T.
[0007]
The calculation of the flow rate, the number of pulses, and the calculation of the pulse period are performed during a certain period T as shown in FIG. 3B, and the number of pulses nt of the calculated pulse period is obtained. Are output during the next fixed period T.
[0008]
FIGS. 3C and 3D are diagrams for explaining the pulse output output during a fixed period T. FIG. Since individual pulses that are output are turned on and off using a microprocessor (timer) interrupt, there is a minimum unit for the on time and off time, and this is the minimum resolution of the pulse output (micro Assuming that the minimum pulse output interrupt unit (Tw) of the processor is Tw, the on time and off time of the pulse are each an integral multiple of the minimum resolution Tw.
[0009]
As shown in FIG. 3 (C), in the pulse period a × Tw (a is an integer equal to or greater than 2) calculated as the number of pulses nt to be output for a certain period T, the pulse output pause at time t A situation can occur. The pulse pause time t in this case is t = T−a × Tw × nt.
[0010]
Therefore, if the pulse period is increased by one unit such as (a + 1) × Tw so as to eliminate the pulse pause state, all the calculated number of pulses are output in the constant period T as shown in FIG. It can happen that you can't. The time t ′ when the pulse cannot be output is t ′ = (a + 1) × Tw × nt−T.
[0011]
In short, if one type of a × Tw or (a + 1) × Tw is used as the pulse period, the number of pulses calculated during the fixed period T without the presence of the pulse output pause state is eliminated. It is not possible to output all of. For example, if the sampling period T = 250 msec, the number of pulses to be output nt = 101, and the minimum resolution Tw = 1 msec of pulse output, a = 2 and a + 1 = 3. At this time, t = 48 msec and t ′ = 53 msec. That is, either a 48 msec pulse pause state or a 53 msec pulse non-output state occurs.
[0012]
Obviously, the number of pulses is not an accurate representation of the flow value in the absence of a pulse output condition. When there is a pulse output pause state, on the receiving side, when counting the number of pulses per unit time and outputting the instantaneous flow rate value, the count value may not accurately display the flow rate value depending on how the unit time is taken. Become.
[0013]
[Problems to be solved by the invention]
Therefore, the present invention solves such a problem, and when outputting a number of pulses representing a measured value within a certain period, the pulse non-output state is not generated and the pulse pause period is negligibly small. The purpose is to do.
[0014]
[Means for Solving the Problems]
In order to transmit the signal measured by the measuring device, the pulse frequency signal output method using the microprocessor of the present invention converts the value of the measurement signal into the number of pulses per fixed period proportional to the value, and interrupts the microprocessor. Output using. A measurement value is calculated for every fixed period, and the calculated measurement value is converted into the number of pulses to be output. Assuming that the number of converted pulses is output during a certain period, one pulse period larger than the period obtained by dividing this certain period by the number of converted pulses, and one smaller pulse period, Two kinds of pulse periods, each of which is an integer multiple of the minimum resolution of the pulse output, are obtained. The number of pulses to be output for each of the two types of pulse periods is calculated so that the pulse pause time until the next fixed period after outputting all the converted number of pulses is as small as possible. And the pulse which has each two types of pulse periods is output by the calculated number of pulses.
[0015]
Further, the pulse frequency signal output device using the microprocessor of the present invention converts the value of the measurement signal into the number of pulses per fixed period proportional to the measurement signal in order to transmit the signal measured by the measurement device. The interrupt is output using a measured value calculation unit, a pulse number calculation unit, a pulse period two-type calculation unit, and a pulse number calculation unit for each period. A measurement value calculation part calculates a measurement value for every fixed period. The pulse number calculation unit converts the calculated measurement value into the number of pulses to be output. The two types of pulse period calculators assume that the number of converted pulses is output during a certain period, one pulse period larger than the period obtained by dividing this certain period by the number of converted pulses, and a smaller number Two types of pulse periods, each of which is an integer multiple of the minimum resolution of the pulse output, are obtained. The pulse number calculation unit for each period should output every two kinds of pulse periods so that the pulse pause time until the next fixed period after outputting all the converted number of pulses is as small as possible. Calculate the number of pulses. And the pulse which has each two types of pulse periods is output by the calculated number of pulses.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
The present invention can be applied to a technique for transmitting a signal measured by a measuring device such as a Coriolis mass flow meter. As described above with reference to FIG. 4, the flow meter electronics 10 supplies a drive signal to the drive device of the Coriolis mass flow meter main body 1 and signals from the left sensor and the right sensor of the Coriolis mass flow meter main body 1. To detect the phase difference proportional to the Coriolis force. The flow meter electronics 10 has a microprocessor and calculates a mass flow value based on the detected phase difference. The calculated measurement value is output in an analog form and in a digital form, and the mass flow value that is the measurement value is combined with a downstream apparatus, and therefore has a pulse having a frequency representing the measurement value. Although output as a signal, the present invention is applied to the output of this pulse signal.
[0017]
The downstream device that has received the pulse signal can obtain the instantaneous mass flow value by counting the number of pulses per unit time of the pulse, and obtain the total mass flow rate by integrating the number of pulses. be able to.
[0018]
FIG. 1 is a block diagram of a pulse frequency signal output unit provided in the flowmeter electronics shown in FIG. This pulse frequency signal output unit converts a measured value (flow rate value) from a measured value (flow rate value) into a pulse frequency signal having a pulse number per unit time proportional thereto.
[0019]
As shown in the drawing, first, in the flow rate calculation unit 12, for example, a flow rate is calculated for each constant cycle (sampling cycle) T as a measurement value. The calculated flow rate value is converted into a pulse number nt to be output by the pulse number calculation unit 13. The above operation is the same as that described with reference to FIG.
[0020]
Next, according to the present invention, the two types of pulse periods are calculated by the two types of pulse period calculation unit 15 as outputting the calculated number of pulses nt during a certain period T. As described above, the pulse period must be an integral multiple of the minimum resolution Tw of the pulse output, considering that it is performed using a microprocessor interrupt.
[0021]
Because of this limitation and the pulse period cannot take a continuous value, the pulse period cannot always match T / nt. Therefore, the present invention makes the pulse pause period as small as possible by using any two of a period larger than T / nt and a small period. However, since it is not desirable that there is a large difference between the two pulse periods used, the present invention preferably uses two consecutive pulse periods. The pulse period must be two, one larger than T / nt and one smaller.
[0022]
Specifically, it is possible to select two integers a and a + 1, where a is an integer obtained by rounding down the fractional part of T / (nt × Tw). That is, the two types of pulse period calculation unit 15 calculates a × Tw and (a + 1) Tw as two types of pulse periods. Expressed by the formula, there is a relationship of a × Tw ≦ T / nt ≦ (a + 1) Tw.
[0023]
Next, the number-of-pulses calculation unit 16 for each period calculates the number of pulses na and nb to be output for every two calculated pulse periods a × Tw and (a + 1) Tw. The pulse numbers na and nb are selected so that no pulse non-output state occurs and the pulse output pause period is minimized.
[0024]
First, nb is selected as the largest integer that satisfies the following condition. That is, it is selected as nb ≦ (T−a × Tw × nt) / Tw. In short, as described with reference to FIG. 3 (C), when the pulse period of all the pulses nt is set to a × Tw, a pulse pause time t is generated, which corresponds to this pulse pause time t. Therefore, the pulse pause time t is eliminated by increasing the pulse period by one unit to (a + 1) Tw. When nb is obtained in this way, na is then obtained as na = nt -nb.
[0025]
FIG. 2 illustrates the output of such two types of pulses. After outputting the pulse number na of the pulse period a × Tw calculated as described above, the pulse number nb of the pulse period (a + 1) Tw is output. At that time, a slight pulse pause time t occurs, but it is much smaller than the above-described conventional technique, and even if it is shifted to the maximum, it is only smaller than Tw. Expressed as an equation, t = T−a × Tw × na− (a + 1) × Tw × nb.
[0026]
For example, similarly to the above-described example, when the sampling period T = 250 msec, the number of pulses to be output nt = 101, and the minimum pulse output resolution Tw = 1 msec, a = 2 and a + 1 = 3. At this time, na = 53, nb = 48, and t = 0 msec.
[0027]
Note that the order in which the pulses having two types of pulse periods are output is arbitrary. As illustrated, after the output of one pulse period is completed, the pulse of the other pulse period can be output, but each pulse is output until the output of the smaller pulse is completed. It can also be output alternately.
[0028]
【The invention's effect】
Since the present invention calculates the number of pulses to be output for each of the two types of pulse periods using the two types of pulse periods, until the next fixed period after outputting all of the calculated number of pulses. Can be made as small as possible.
[0029]
The present invention does not cause a pulse non-output state and makes the pulse output pause state as small as possible, and on the receiving side, counts the number of pulses per unit time and outputs an instantaneous flow rate value. It is possible to receive and display accurately.
[Brief description of the drawings]
1 is a block diagram of a pulse frequency signal output unit provided in the flowmeter electronics shown in FIG. 4;
FIG. 2 is a diagram illustrating the output of two types of pulses according to the present invention.
FIG. 3 is a diagram for explaining the operation of a conventional pulse frequency signal output unit that converts a measured value into a pulse frequency signal using a microprocessor.
FIG. 4 is a diagram for explaining the operation of a conventional general Coriolis mass flow meter.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Coriolis mass flowmeter main body 10 Flowmeter electronics 12 Flow rate calculation part 13 Pulse number calculation part 14 Pulse period 1 type calculation part 15 Pulse period 2 type calculation part 16 Pulse number calculation part for every period

Claims (4)

In order to transmit the signal measured by the measuring device, a pulse frequency signal using a microprocessor that converts the value of the measurement signal into a pulse number per fixed period proportional to the measured signal and outputs a pulse using a microprocessor interrupt In the output method,
Calculate the measurement value at regular intervals, convert the calculated measurement value to the number of pulses to be output,
Assuming that the number of converted pulses is output during a certain period, one pulse period larger than the period obtained by dividing this certain period by the number of converted pulses, and one smaller pulse period, Find two types of pulse periods, each of which is an integer multiple of the minimum resolution of the pulse output,
Calculate the number of pulses to be output for each of the two types of pulse periods so that the pulse pause time until the next fixed period after outputting all the converted number of pulses is as small as possible,
Outputting each of the pulses having the two types of pulse periods for the calculated number of pulses,
A pulse frequency signal output method comprising: 2. The pulse frequency signal output method according to claim 1, wherein the two kinds of pulse periods consist of two consecutive possible pulse periods. In order to transmit the signal measured by the measuring device, a pulse frequency signal using a microprocessor that converts the value of the measurement signal into a pulse number per fixed period proportional to the measured signal and outputs a pulse using a microprocessor interrupt In the output device,
A measurement value calculation unit for calculating a measurement value at regular intervals;
A pulse number calculation unit for converting the calculated measurement value into the number of pulses to be output;
Assuming that the number of converted pulses is output during a certain period, one pulse period larger than the period obtained by dividing this certain period by the number of converted pulses, and one smaller pulse period, Two types of pulse period calculation units for obtaining two types of pulse periods, each of which is an integer multiple of the minimum resolution of the pulse output;
The number of pulses to be output for each of the two types of pulse periods is calculated for each period so that the pulse pause time until the next fixed period after outputting all the converted number of pulses is as small as possible. A pulse number calculation unit;
And a pulse frequency signal output device that outputs the pulses each having the two types of pulse periods for the calculated number of pulses. The pulse frequency signal output device according to claim 3, wherein the two kinds of pulse periods are composed of two consecutive pulse periods.

Images