JPS5819116B2 - 2 Senshikidensouki - Google Patents

Description

[Detailed Description of the Invention] This invention multiplies the current level normally used in various two-wire transducers such as differential pressure displacement transducers, capacitance displacement transducers, temperature transducers, and pH converters by a certain factor. The present invention relates to a two-wire transmitter that can output signals.

There are 4 unified signal systems used in electronic automatic control systems.
~20 mA is becoming the mainstream.

However, 1-5 mA, 2-10 mA, and 10-5
Those with a 0mA signaling system are still in use.

In particular, since the 10 to 50 mA signal system has been the mainstream in the past, many plants using instruments with this signal level are actually operated.

In such a situation, it is conceivable to replace the entire electronic control device with a new one using a 4-20 mA signal system, but doing so would involve a lot of expense.

On the other hand, in terms of lifespan, the lifespan of the converter is shorter than that of the power supply.

Therefore, when replacing only the converter part, the conventional lO ~ 50
It is possible to make a mA type converter and replace it, but it is not a good idea to go to the trouble of making an old type one.

In addition, even if higher measurement accuracy than before is required and a new type of converter is required, it is economical to use conventional types for parts other than the converter. It is true.

However, in these cases, conventionally the circuit constants are different for each converter.

That is, transmission equipment for 4 to 20 mA and 10 to 50 mA was prepared and only the converter was replaced.

Therefore, there are many models to prepare, which makes maintenance both inconvenient and expensive.

The present invention provides a two-wire transmitter that can easily multiply the signal level by a certain number of times as needed without preparing dedicated models for each type of transmission equipment with different signal levels. It is.

According to the invention, a two-wire main conversion unit;

A 2-wire slave conversion unit capable of multiplying the conversion output level by a certain amount is built into one housing, and this 2-wire slave conversion unit is a 2-wire slave conversion unit with the same configuration as the 2-wire main conversion unit. The same power source as the operating power source from the receiving side for the main conversion unit.

It can be operated by

This 2-wire transmitter can transmit the first unified current signal (4 to 20 mA) output of the 2-wire main converter unit directly to the 5 receiving side, or this 2-wire slave Second unified current signal output (10 series ~
It is also possible to multiply the output current to 50 mA and transmit it to the receiving side, and the desired output current level can be obtained depending on the location where it is used, and there is no need to provide a separate power supply, making the configuration simple. be able to.

Next, an embodiment of a two-wire transmitter according to the present invention will be described with reference to the Σ plane of FIG.

In the figure, reference numeral 1 indicates a two-wire main converter unit having a normal configuration.

The main conversion unit 1 has a + side power terminal 2a and one side power terminal 2b, and is a capacitive displacement converter, a differential pressure type displacement converter, a temperature converter, or the like.

In this example, a well-known temperature transducer is shown.

That is, OA is a high gain operational amplifier, Q2 is a constant current device,
Zl is a Zener diode for stabilizing the power supply voltage applied to the operational amplifier OA and the reference bias voltage applied to the input terminal.

The reference voltage obtained across the zener diode Z1 is divided by the resistors Rt and Ra including the temperature sensing resistor, and this divided voltage is applied to the inverting input terminal, and the voltage of the zener diode Z1 is applied to the non-inverting input terminal. The sum of the voltage and the voltage drop occurring across the feedback resistor Rf is divided by the resistors Rb and Rc and provided.

Ql is an output transistor driven by the output of the operational amplifier OA and outputs the first unified current signal Ii (for example, 4 to 20 mA
) minus the constant current value due to Q2.

Note that Z2 is a Zener diode connected in series to the emitter of the output transistor Q1, and is used to operate the operational amplifier OA at an appropriate output level with a high gain.

Now, the first unified current signal is generally 11~5.1 mA.
It is expressed as

This two-wire main conversion unit 1 is operated by a power supply 3 on the receiving side, and both ends of the power supply 30 are connected through transmission lines 4a and 4b.
Moreover, it is connected to the power supply terminals 2a and 2b of the two-wire main conversion unit 1 through the two-wire sub-conversion unit 6 inserted in particular according to the present invention.

A load resistor 5 is connected in series to the transmission line 4b on the receiving side, and a process variable can be detected from the voltage signal obtained at the load resistor 5.

The 2-wire slave conversion unit 6 multiplies the output current 11 to 5 I 11TIA of the 2-wire main conversion unit 1 by a fixed amount, that is, it converts the level to a current of 12 to 512 mA and outputs it to the load resistor 5. supply

This unit 6 has a power terminal 2a on the two-wire main conversion unit 1 side.

The output current of the two-wire main conversion unit 1 (
a first current detection resistor 10 that detects a first unified current signal)
and a current detection resistor 16 for detecting the output current of the two-wire slave conversion unit 6 are connected in series between terminals 7b and 8b.

Both ends of the first current detection resistor 100 are connected to a non-inverting input terminal and an inverting input terminal of an operational amplifier 13 through high resistance value resistors 11 and 12, respectively.

The voltage across the first current detection resistor 100 is amplified by the operational amplifier 13, and its output is supplied to the base of the transistor 140 and converted into a current.

The collector of the transistor 14 is connected to one of the output terminals 8a, and the emitter is connected to one of the output terminals 8a through a resistor 15 as necessary.
It is connected to the connection point of the first current detection resistors 10 and 12.

The connection point A of the first current detection resistors 10 and 15 is the second
It is connected to the other output terminal 8b through the current detection resistor 16.

The connection point between the second current detection resistor 16 and the output terminal 8b is connected to the non-inverting input terminal of the operational amplifier 13 through a high resistance value resistor 18.
The voltage signals generated at 6 are supplied to operational amplifier 13 in a direction to balance each other, and negative feedback is provided.

Therefore, the voltage obtained at the first current detection resistor 10 is amplified by the transistor 14, and the output current is transmitted from the output terminal 8b through the second current detection resistor 16 to the transmission line 4b by multiplying the first unified current signal by a certain number. It is supplied to the load resistor 5 as a second unified current signal multiplied by .

In order to supply the operating voltage to the operational amplifier 13 and the power supply voltage to the two-wire main conversion unit 1, the collector and emitter of the transistor 20 are connected between one of the output terminals 8a and one of the input terminals 7a in the figure. connected,
Its base is connected through a zener diode 21 to a resistor 1
5 and 10, and the transistor 200
A resistor 22 is connected between the base and collector, and a so-called constant voltage circuit 23 is configured.

The constant voltage output from the emitter of the transistor 20 is connected to one end of the power supply terminal of the operational amplifier 13, and also to the Zener diode 21.
The connection point of the resistor 10 and the resistor 10 is connected to the other end of the power supply terminal of the operational amplifier 13.

Therefore, the operational amplifier 13 operates with the voltage difference between the voltage of the Zener diode 21 and the voltage between the base and emitter of the transistor 200.

The resistance values of the resistors 12 and 18 are set to be sufficiently high so that the current flowing through them can be ignored with respect to the output current (first unified current signal) Ji of the two-wire main conversion unit 1, and the resistance values of the resistors 11 The respective resistance values of the resistor 18 and the resistor 18 are set to be equal, and each resistance value is set to R.

Then, the output current of the two-wire slave conversion unit 6 is ■.

, and the resistance value of the first current detection resistor 10 is R1, and the resistance value of the second current detection resistor 16 is R2.

The output current ■. are the emitter current of the transistor 14, the operating current of the operational amplifier 13, and the Zener diode 21.
, and the first unified current signal Ii.

Now, considering point A as the reference potential point, the first current detection resistor 1
The voltage generated at 0 (voltage obtained at input terminal 7b) is +
It is l1-R1.

Similarly, the second current detection resistor 16 is set with point A as the reference potential point.
The voltage generated is ■.

flows from point A toward output terminal 8b, so -■.

-R2. These voltages are led to the non-inverting input terminal (point B) of the operational amplifier 13 via a high resistance 11.18.

Here, assuming that the high resistances 11.18 have the same resistance value R as described above, the minute current i flowing through these resistances becomes 1=■i°R·+l0R2.

R Therefore, the voltage drop that occurs across the resistor 11 is i-: [(= I iR1 + l0R2, and the voltage Eb at point B is E, = IiR1 considering point A as the reference potential point.
−■iR1+1oR2=■1R0−■oR2(,)2.

On the other hand, the inverting input terminal C point of the operational amplifier 130 is connected to the point A via the high resistance 12, and if the input impedance of the operational amplifier 13 is high, the input current can be ignored, so no voltage drop occurs across the resistance 12. , the potential Ec at point 0 is equal to the reference potential at point A, which is zero potential.

Therefore, the operational amplifier 13 amplifies the voltage Eb in equation (1),
The amplified output drives output run sister 4;

increase. ■The voltage of the second current detection resistor 16 due to an increase in o.

-R increases in the negative direction with respect to point A and acts to reduce the value of Eb in equation (1), so the resistors 16.18 form a negative feedback loop.

Here, if the gain of the operational amplifier 13 is sufficiently large, the voltage Eb at the non-inverting input terminal B of the operational amplifier 13 will be approximately equal to the voltage Ec (zero potential) at the non-inverting input terminal C due to the effect of this negative feedback. Become.

That is, E, =■1R1-■oR2=.

From this, Ii'R1=Io'R2, and the following relationship is obtained: ■o=几・Ii (2)2 For example, the 1st series - current signal engineer 1=11
-511 (4-20mA)■.

-12~5■2 (10~50mA) To convert to the second unified current signal, set the ratio of the resistance values of the first current detection resistor 10 and the second current detection resistor 16 to ' = 2.5. All you have to do is select 2.

This two-wire slave conversion unit 6 is a two-wire main conversion unit 1.
It is operated by the current supplied from the receiving side power supply 3, and the bias current difference, that is, I2-1
1 (10mA-4mA=6mA), the operational amplifier 13, diode 21, and transistor 4 are made to operate.

Actually, since there is an offset voltage in the operational amplifier 13, the zero point shifts by 1 degree from the value of equation 2), but this can be adjusted on the two-wire main conversion unit 1 side.

A span error also occurs depending on the accuracy of the resistance values of the resistors 10, 16, 11.18, but this can also be adjusted on the two-wire main conversion unit 1 side.

FIG. 2 shows a case where the two-wire slave conversion unit 6 is capable of zero point adjustment and span adjustment.

In addition, in this example, the constant voltage circuit 23 is simply composed of a Zener diode 21, an RC filter consisting of a resistor 30 inserted in series with the transmission line 4a, and a capacitor 31 inserted between the transmitters 4a and 4b. This is the case when configured as follows.

A series circuit of a resistor 33 and a zener diode 34 is connected to both ends of the zener diode 210, a voltage dividing circuit of resistors 35 and 36 is connected to both ends of the zener diode 34, and the voltage dividing point is connected to the resistor 37. The inverting input terminal of the operational amplifier 13 is connected through the inverting input terminal of the operational amplifier 13.

Further, a variable resistor 38 is connected in parallel with the Zener diode 34.

The movable element is connected to the non-inverting input terminal B of the operational amplifier 13 through a resistor 39.

One end of the first unified current detection resistor 10 is connected to the connection point between the resistor 36 and the Zener diode 21, and the other end is connected to the input terminal 7b. Connected to inverting input terminal B.

The negative side of the power supply terminal of the operational amplifier 13 is connected to the output terminal 8b, the resistor 16 is a variable resistor, and the movable element thereof is connected to the non-inverting input terminal B of the operational amplifier 13 through the resistor 18.

By adjusting the variable resistor 38, the zero point, ie when the signal to be converted in the two-wire main conversion unit 1 is zero (I 1 = 11), the output current ■.

Adjust so that it becomes I2.

Further, the movable element of the variable resistor 16 is adjusted so that 12 to 5<2> is within a predetermined range <2>, that is, I1 is adjusted to a predetermined value.

Since the output current of the two-wire sub-conversion unit 6 is relatively large, the usage conditions may become severe if only one transistor 4 is used.

Therefore, this example shows a case where two transistors 4a and 14b are used in parallel.

Some operational amplifiers 13 have a current consumption that fluctuates by only about 240 to 300 μ8 when the supply voltage changes from 10 to 40 V. If you use such an operational amplifier, the current change in the operational amplifier 13 due to power supply fluctuations will be reduced. Conversion output current 1
It is negligible for 0-50mA.

Therefore, in such a case, the first
In the figure, the negative side of the power supply is connected to the negative terminal side of the operational amplifier 13, and this connection point is connected to the resistor 16 to output terminal 8b.
However, without doing such a thing, as shown in FIG. It is also possible to directly connect the power supply voltage to the power supply voltage to prevent negative feedback from occurring due to fluctuations in the power supply voltage.

The two-wire main conversion unit 1 and the two-wire slave conversion unit 6 can be housed in a common housing 44 so as to be removable as necessary, as shown in FIG.

A terminal box 45 is connected to the housing 44, and terminals 46 are connected to the transmission lines 4a and 4b, respectively, inside the terminal box.
a.

46b is provided.

If the operating power supply and receiver on the receiving side for the two-wire main conversion unit 1 are of an old type, that is, those with a signal format of 10 to 50 mA, the connections shown in dotted lines in Fig. 3, that is, Fig. 1, should be made. , terminal 2a as shown in FIG.
, 2b.

Connect input terminals 7a, 7bs and output terminals 8a, 8b.
The wire slave conversion unit 6 may be electrically inserted and connected, and the terminals 46a and 46b may be directly connected between the five transmission lines 4a and 4b.

If the receiver and power supply on the receiving side are of the 4 to 20 mA type, connect them as shown in the solid line in Figure 3 and connect the transmission line and terminal 46.
a.

The connection of 46b may be 5 as is.

In other words, the terminal 46a. Connect terminal 'l a t 2 b to 46b.
All you have to do is connect them to each other.

In this way, it is sufficient to simply change the terminal connections inside the housing 44 depending on whether current conversion is required or not. There is no need to provide a special power source, and if the conversion unit 6 is inserted and connected between the two-wire main conversion unit 1 and the terminals 4sa and 4eb, the conversion unit 6 will automatically operate.

It can be used for any signal level type by terminal connection conversion.

Therefore, in the conventional old 10-50 mA type electronic automatic control device, because the two-wire converter has reached the end of its service life, or to improve measurement accuracy, another 10-50 mA type
When replacing the A signal format 2-wire main converter with a 2-wire main converter, it is sufficient to use the 2-wire transmitter of the present invention and connect it as shown in the dotted lines as shown in Figure 3, which eliminates all the conventional equipment. It is economical as there is no need to replace it.

After this replacement, if the main power supply 3 on the receiving side or the receiver reaches the end of its service life, use a new 4 to 20 mA type one, and at the same time, connect the connections inside the housing 44 as indicated by the solid line in Figure 3. Just convert the connection as shown, 2
There is no need to replace the wire converter side.

Note that in FIG. 3, the terminal 46a. 46b may be provided not only in the terminal box but also directly in the housing 44.

According to the two-wire slave conversion unit of the type shown in FIG. 1, as explained earlier, the relationship between the current ■ and I2 is the resistance value R2.
This is a relationship determined by the ratio of R1 and R1, that is, the output current of the two-wire slave conversion unit 6.

is related only to the input current Ii and the resistance values R2 and R1, and is related to the operational amplifier 13, transistor 14, and Zener diode 2.
It has a feature that it is independent of the operating current of transistor 1 and is not affected by temperature changes or changes in the current amplification factor hFE of the transistor 14.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing one example of a two-wire transmitter according to the present invention, FIG. 2 is a connection diagram showing another example, and FIG. 3 is a route diagram of its mechanical configuration. 1...2-wire main conversion unit I', 2a, 2b.
...Power terminal, 3...Power supply, 6...
...2-wire slave conversion unit, 7a, 7b...Input terminal, 8a, 8b...Output terminal, 10...
...First resistor, 14... Output transistor, 16... Second resistor, 11, 18...
...The voltage signal generated in the first and second resistors is transferred to the operational amplifier 1.
High resistance means supplied to the input side of 3, 20...transistor constituting a constant voltage circuit, 21.・00. - Constant voltage diode that constitutes the constant voltage circuit, 23...
- Constant voltage circuit, 38...variable resistor for zero point adjustment.

Claims (1)

[Claims] 1 A pair of power supply terminals, an operational amplifier supplied with power from these terminals and inputting signals related to the process variable to be measured and signals related to the current flowing through the power supply terminals; a two-wire main conversion unit comprising an output transistor driven by an output to vary said current, and transmitting a first unified current signal related to said process variable via said terminal; A pair of input terminals each connected to a pair of power supply terminals of the main conversion unit, a pair of output terminals to which a series circuit consisting of a power supply and a load resistor is connected, and one of these output terminals and one of the above input terminals. a constant voltage circuit connected to the constant voltage circuit; an operational amplifier driven by the output of the constant voltage circuit; and an operational amplifier driven by the output of the operational amplifier to change the current flowing through the output terminal to maintain a constant value of the first unified current signal. a first resistor connected between the other of the input terminals and the other of the output terminals and converting the first unified current signal into a voltage signal; 2, comprising: a second resistor for converting a current signal associated with a flowing second unified current signal into a voltage signal; and means for supplying a voltage signal developed across the fourth and second resistors to an input of the operational amplifier; A two-wire transmitter consisting of a wire slave conversion unit and ).