JPH04220895A - Terminal adjustment device in data transmission system - Google Patents

Abstract

PURPOSE:To realize the terminal equipment adjustment device in the data transmission system in which the data transmission system is formed with simple configuration and an error of a measured value is corrected. CONSTITUTION:A terminal equipment is provided with a circuit having a comparator 31 to monitor a power supply voltage sent onto a bus, a relay activated by the output of the comparator 31, and an oscillator 37 outputting a resistance change of a thermister 35 at the temperature measurement state when no relay is activated as a frequency change and outputting a reference frequency corresponding to a reference resistor connected in place of the thermister 35.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a terminal adjustment device in a data transmission system, and more particularly to a terminal adjustment device in a data transmission system in which terminal devices are adjusted under control from a center device.

0002

2. Description of the Related Art Conventionally, data transmission systems have been known in which a center device and a terminal device are connected via a bus, and a signal measured by the terminal device is transmitted to the center device. The terminal device of such a system is equipped with a microcomputer, and data transmission is controlled by the microcomputer. Furthermore, if an error occurs in the measured value due to deterioration or drift in the circuit system, the measured value is automatically compensated by the action of the microcomputer.

0003

[Problems to be Solved by the Invention] As mentioned above, when a system is configured using a terminal device equipped with a microcomputer, a multi-wire bus is required to transmit bit strings in parallel, and the terminal device There was a problem that the circuit configuration became complicated.

[0004] Therefore, an object of the present invention is to provide a terminal adjustment device for a data transmission system that can configure a data transmission system with a simple configuration and can correct errors in measured values. .

[0005]

SUMMARY OF THE INVENTION The present invention is a terminal adjustment device in a data transmission system in which a center device and a terminal device are connected via a bus.

[0006] The center device includes a power supply output means for outputting the power supplied to the terminal device to the bus, and a voltage variation means for varying the power supply voltage of the power supply output means in order to instruct adjustment of the terminal device. .

[0007] The terminal device performs necessary measurements and outputs a signal to be transmitted to the center device, a detection device detects a change in the power supply voltage supplied via the bus, and a detection device. and signal adjustment means for adjusting the signal output means in response to the output.

[0008]

[Operation] The center device according to the present invention supplies power supply voltage to the terminal devices via the bus. When instructing adjustment of the terminal device, the center device varies the power supply voltage supplied to the bus within a range that does not cause any trouble to the terminal device. When the terminal device detects a predetermined variation in the power supply voltage, the terminal device adjusts the signal output means that outputs a signal to be transmitted to the center device.

[0009]

[Embodiment] A data transmission system for transmitting temperature data will be described below as an embodiment of the present invention, but the present invention is not limited to this. It should be pointed out in advance that it can be applied to any system.

FIG. 1 is a diagram showing the configuration of a data transmission system according to an embodiment of the present invention. First, the general configuration and characteristics of the system shown in FIG. 1 will be explained.

In FIG. 1, the data transmission system includes a center device 10, a two-wire bus 15, and a plurality of terminal devices 21 connected to the center device 10 via the bus 15.
, 22...2n. The center device 10 has a power supply section and generates the power necessary for the terminal devices 21 to 2n. Power source power is given to the terminal devices 21 to 2n via the bus 15. The terminal devices 21 to 2n constantly measure the temperature and transmit the measurement signal to the center device 10 via the bus 15.

An example of the circuit configuration of the main parts of the terminal devices 21 to 2n is shown in FIG. As shown in FIG. 2, the terminal devices 21 to 2n are provided with a thermistor 35 as a temperature measuring element. The resistance change of the thermistor 35 is applied to an oscillator (OSC) 37. The oscillator 37 outputs a signal whose frequency changes according to the resistance change of the thermistor 35. In other words, changes in temperature are converted into changes in frequency. The temperature signal output from oscillator 37 is bus 1
5 to the center device 10. The center device 10 converts the signals transmitted from the terminal devices 21 to 2n into voltages, further converts them into digital data using an A/D converter (not shown), and displays the digital data on a display unit (not shown) or the like.

Since this system transmits temperature changes as continuous frequency changes, it has the following general characteristics (1) to (4).

(2) Continuous temperature changes can be obtained. ■It can be seen that the terminal equipment is normal because the signal is being transmitted.

[0015] The terminal equipment is very simple in configuration and is therefore inexpensive. This system is further characterized by compensating for drift and gain deterioration with a simple configuration due to the specific configuration described below.

The center device 10 has a control section that changes (reduces) the value of the power supply voltage superimposed on the bus to an extent that does not change the circuit operation when adjusting the terminal devices 21 to 2n. For example, when performing zero point compensation, the center device 10 lowers the power supply voltage on the bus 15 by a certain width for a certain period of time. The terminal devices 21 to 2n enter a zero point compensation state when it is detected that the predetermined voltage drop in the power supply voltage continues for a certain period of time.

The terminal devices 21 to 2n are provided with a comparator 31 for monitoring the voltage of the power supply. When the voltage at one end 311 of the comparator 31 to which the divided voltage of the power supply voltage is input is lower than the voltage at the other end 312 to which the reference voltage is input, the output from the output end 313 of the comparator 31 becomes high level. Note that one end 311 of the comparator 31 is connected to a capacitor 38 in order to prevent the comparator 31 from operating due to a momentary voltage drop due to noise or the like.
connected to. When the output of comparator 31 becomes high level, relay 32 operates. As a result, the relay contact that was connected to the terminal 33 on the thermistor 35 side during temperature measurement is switched to the terminal 34 on the reference resistor 36 side.

During temperature measurement, the resistance change of the thermistor 35 is input to the oscillator 37, and a signal whose frequency changes according to the temperature change is output from the oscillator 37. However, during zero point compensation, the relay contact is connected to the terminal 34. By switching to the reference resistor 3 instead of the thermistor 35,
6 is connected, and the oscillator 37 outputs a signal with a reference frequency. As a result, the center device 10
Calculation and compensation are performed using the reference frequency signal as the 0 point.

By detecting the power supply voltage in two stages, zero point compensation and gain compensation can be performed.

FIG. 3 is a diagram showing an example of a circuit configuration having such a function. In FIG. 3, terminal devices 21 to 2
A first comparator 41 and a second comparator 42 are provided at n. The reference voltage of the first comparator 41 is set higher than the reference voltage of the second comparator 42. When the power supply voltage becomes lower than the first reference voltage, the output of the comparator 41 becomes a high level, and when the power supply voltage further decreases and becomes lower than the second reference voltage, the output of the comparator 42 becomes a high level. become. When the output of comparator 41 becomes high level, relay 5
1 works. When the output of the comparator 42 becomes high level, the relay 52 is further activated.

[0021] When only the relay 51 operates, the contact 43 that was previously connected to the bus 152 opens, and
Since the contact 44 is connected to the bus 152 and thereby the first reference resistor 47 is connected instead of the thermistor 35, the signal at the reference frequency corresponding to the low temperature is transmitted to the oscillator 37.
is output from. Thereby, as shown in FIG. 4, compensation for the low temperature (0 point) is performed.

Further, when both relays 51 and 52 operate, contact 45 is further opened and contact 46 is opened.
is connected to the bus 152, and the first reference resistor 47 and second reference resistor 48 connected in parallel are connected instead of the thermistor 35, so that the signal of the reference frequency corresponding to high temperature is is output from the oscillator 37. As a result, as shown in FIG. 5, compensation at high temperature (H) is performed, and gain compensation is possible as well as zero point compensation.

By setting the voltage level in two stages in this way, it is possible to compensate not only the zero point but also the gain.

[0024]

As described above, according to the present invention, it is possible to adjust the terminal device by controlling from the center device with a simple configuration.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a data transmission system according to an embodiment of the present invention.

FIG. 2 is a diagram showing a circuit configuration of main parts of the terminal device shown in FIG. 1;

FIG. 3 is a diagram showing another circuit configuration of the main parts of the terminal device shown in FIG. 1;

FIG. 4 is a graph for explaining 0-point compensation.

FIG. 5 is a graph for explaining zero point compensation and gain compensation.

[Explanation of symbols]

10 Center equipment 15 Bus 21, 22~2n Terminal equipment 31 Comparator 35 Thermistor 36 Standard resistance 37 Oscillator

Claims (1)

[Claims] 1. A terminal adjustment device in a data transmission system in which a center device and a terminal device are connected via a bus, wherein the center device controls the power supply supplied to the terminal device via the bus. The terminal device is equipped with a power output means for outputting to the bus, and a voltage variation means for varying the power supply voltage of the power output means in order to instruct adjustment of the terminal device. a signal output means for outputting a signal to be transmitted to the device;
Terminal adjustment in a data transmission system, comprising a detection means for detecting a change in the power supply voltage supplied via the bus, and a signal adjustment means for adjusting the signal output means in response to the output of the detection means. Device.