JPS61223623A - Multipoint temperature measuring device - Google Patents

Abstract

PURPOSE:To reduce an error voltage due to noise and to remove restrictions on terminal arrangement by disconnecting all points of a resistance bulb input line from an internal circuit by a switch, and setting all scanner switches to the common scanner system. CONSTITUTION:In case that a thermocouple TC1 is selected, a thermoelectromotive force generated in the thermocouple TC1 is applied to an operational amplifier U1 and its value is measured thereafter by setting a switdh SWs1 to the turn-on state and setting switches SWa, SWd, SWe, SWb, and SWs2-SWsn to the turn-off state and setting a switch SWc to the T side. Since scanner switches SWs2-SWsn are all turned off at this time, the dielectric strength between channels is secured. Since operation reference resistance selecting switches SWd and SWe are turned off also, the low-side line of the input of the thermocouple is not connected to the resistance bulb line. As the result, a normal mode voltage Vnm is equal to VcmX(RL1)/(RL1+ZL) with respect to a common mode voltage Vcm when the voltage Vcm exists in the thermocouple TC1, and the error voltage Vnm is very low because an impedance ZL to ground of an input circuit is very larger than a signal source impedance RL1 in general use circumstances.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a multi-point temperature measuring device that uses thermocouples and resistance thermometers as inputs, and particularly improves the input circuit portion thereof.

[Conventional technology]

What is the thermocouple in Figure 2? It is a connection diagram of the input circuit part of the multi-point temperature measuring device with l[l+thermal resistance element input. In FIG. 2, C1, TC2-...TCn are thermocouples, PTl, PT2. . . . PTr+ is a temperature measuring resistor. Resistance temperature sensor PT1. PT2. ...PTn
is a 3-wire system with input terminals A and B.

b, and each terminal is connected to the calculation reference resistor Ra.
connected to a common potential point via. SCI is a thermocouple scanner card, SC2 is a resistance thermometer scanner card, S'lt1.5'1lt2.・”5VItn
is a manual switching element for thermocouple, 5Wr1.5Wr2. ...
'JVrn is the scanner switch contact, ■ is the resistance temperature detector PT1. PT2. ... Current source for r'I' n, U
1 to U3 are operational amplifiers, and SWa is a switch for selecting thermocouple input and resistance temperature detector input.

Current source! is input switching element for resistance temperature sensor 5Wr1.5Wr
Resistance temperature detector PT1 via contact C of 2°...5Wrn
．． PT2. ...Connected to PTn.

In the input circuit of the multi-point temperature measuring device having such a configuration, as is well known, the selection switch SWa is turned OFF and the thermocouple scanner switches 5Wt1.5Vt2 . ...5Wt
By sequentially turning on n, thermocouples TC1 and TC2
,...The output of TCn is taken in for the 11th time. The thermocouple output is applied to an operational amplifier U1, and the output of U1 is applied via an A/D converter to an autobalancing circuit (not shown).

On the other hand, turn on the changeover switch SWa to connect the resistance temperature detector scanner switch contact 5Wr1. ! 1iWr2. ...5
By scanning Wrri, the resistance temperature detector PT1.
PT2. . . . The output of PTn is sequentially taken in, and the output of the temperature measuring resistor is sequentially taken out and measured via the Patzfur operational amplifier U2, the differential operational amplifier U3, and the operational amplifier υ1. A multi-point temperature measuring device with such a configuration has already been put into practical use and is well known, but it is as follows (a).

There are two problems with the mouth.

[B] For example, if the common mode voltage Vcm is applied to the thermocouple TC1
When Vnm exists, a normal mode voltage Vnm shown by equation (1) is generated.

Vnm= Vcmx (RLI) / (RL1+(ZL
// Zb))...(1) In formula (1), RLl, signal source impedance ZL, input circuit ground impedance (mainly insulation resistance and stray capacitance between the input circuit and the ground) Zb; Zbl
// Zb2//--// ZbnZbl, Zb2.
・=Zbn; resistance temperature sensor PTI, PT2. - P
This shows the ground impedance of the Tn circuit.

Here, Vcm-100V, RL1=300,
When Zb > IMO, the normal mode voltage becomes 3+++V in Vnm from equation (1). This value appears as an extremely large error in practice.

(b) Since the scanners for thermocouples and RTDs are separated (for each 6-point group), it is not possible to connect the desired type of input to any terminal.

[Problem that the invention seeks to solve]

The present invention eliminates errors caused by noise current caused by the connection of both thermocouple inputs and resistance bulb inputs when a single multi-point temperature measuring device is used in combination, and provides a low-scanner configuration. The object of the present invention is to provide a multi-point temperature measuring device that is not subject to restrictions on the positions of both terminals.

Means for Solving Problems] In order to achieve the above object, the present invention has three terminals, two of which are connected to a thermocouple or a resistance temperature detector, and the remaining one is connected to a thermocouple or a resistance temperature detector. multi-point input terminals are connected in common, each has three switching contacts, two of which scan the output of the thermocouple or resistance temperature detector, and one contact of which is connected to the resistance temperature detector. a scanner switch to which a body current source is connected; a first selection switch for selecting the thermocouple or resistance temperature detector output obtained via the scanner switch; and a first selection switch to which the thermocouple output is applied via the selection switch. a second operational amplifier that has an input resistance and a feedback resistor and calculates and outputs a difference in potential between both ends of the temperature-measuring resistor; and the output of the second operational amplifier is selected by the first selected a second selection switch that is applied to the first operational amplifier when the thermocouple is not selected by the switch; and a calculation reference resistance connected to the common connection terminal of the input terminal via the calculation reference resistance selection switch. It is composed of Examples will be described below.

〔Example〕

FIG. 1 is a circuit diagram of an embodiment of a device according to the present invention.

In the figure, TCl,...TCn are thermocouples, PTI.

...PTn is a resistance temperature detector, A, B, b are input terminals,
Resistance temperature sensor PT1. PT2.・= PTn is connected to input terminals A, B, and b in a 3-wire system, and the terminals are connected in common. In the apparatus shown in FIG. 1, a thermocouple and a temperature measuring resistor such as a PTI are connected to an input terminal at an arbitrary position next to the TCl. SC is a scanner card with thermocouple and resistance temperature detector, 5Ws1.5Ws2.・
...5Wsn is a scanner switch having contacts a, b, and c, respectively, and SWa and 5WbJWc are selection switches for selecting a thermocouple input and a crosstalk resistor input. The selection switch SWc is a double-ended switch and has a terminal T for a thermocouple and a terminal R for a resistance temperature detector. SWd and SWe are arithmetic reference resistance selection switches for the resistance temperature detector, Ra and Rh are reference resistances for arithmetic operation, ■ is a current source for the resistance temperature detector, and U1 to U3 are operational amplifiers.

Input terminals A and B to which thermocouple Tel...TCn is connected
are the scanner switches 5Wsl...S'Ws, respectively.
It is connected to the operational amplifier υ1 via the contacts a and b of n and the terminal T of the selection switch SWc. Resistance temperature detector PT
Input terminals A, B to which I...PTn are connected are connected to contacts a, b of scanner switches 5Vs2...5Wsn and terminal R of selection switch SVc, and the terminals R are connected to operational amplifiers u2. It is connected to operational amplifier U1 via u3. The current source 1 is connected to each contact C of the scanner switches S'1ls2...5Nlsn via a selection switch SWb. The calculation reference resistance Ra is connected to the input terminal S via the calculation reference resistance selection switch SWd, and the calculation reference resistance Rh is connected to the input terminal via the switch Swe. The calculation reference resistance selection switches SWd and SVe each have a plurality of contact points, and this is to reduce the contact resistance of the contact points.

In the multi-point temperature measuring device having such a configuration, first, the case where the thermocouple TCI is selected will be explained as follows. In this case, set each switch as follows.

5Wsl:O)l, SWa;OF
F, SWb;0FFSWc
;T side, 5IFd, SWe;OFF 1SWs2~
511sn; OFF By setting each switch in this way, the thermoelectromotive force generated by the thermocouple TC1 is applied to the operational amplifier υl, and then sent to the A/D converter and then to the automatic balance circuit (not shown). ) and its value is measured.

At this time, other scanner switches 511s2...5W
Since sn is all OFF, the Ill voltage of these switches ensures the withstand voltage between the channels. Also, since the calculation reference resistance selection switch SWd, S''lc+ is OFF, the LOW side line of the thermocouple input is not connected to the resistance temperature detector line.As a result, the thermocouple TCI is connected to the thermocouple input as shown in Figure 2. When a common mode voltage Vc exists,
The normal mode voltage Vnm with respect to the common mode voltage Vc■ is expressed by equation (2) in the circuit shown in FIG.

V rv+-V cmx(RLI)/(RLl+ZL)
--(2) Here, in a general usage environment, the ground impedance ZL of the input circuit is extremely large with respect to the signal source impedance RLI, so the error voltage Vnm is This is extremely small compared to the actual case.

Next, a case will be described in which the resistance temperature sensors PTI...PTn are selected. In this case, set each switch as follows.

5Ws2:ON, SWa:0N1SWb;ON
SWc; R@, Swd; ON, SWe;
OFF, S+fs1.5Ws3~5Wsn: OFF
By setting each switch in this way, the resistance temperature detector PTI has a common potential point → calculation reference resistance Ra → calculation reference resistance selection switch SWd → input terminal → resistance temperature detector PTI → scanner switch 5w52 Contact C → selection switch SWb → current source! Current j flows through a path consisting of: Here, if the resistances of the lead wires 11 and 12 connecting the resistance temperature detector PTI to the input terminals A and B are respectively "," and the resistance of the resistance temperature detector PTl is Rtl, then the potential appearing at the output terminal of the operational amplifier U2 is C1 is el-(Rtl+7!r+
Ra) t -・・・・・” (3
). Furthermore, the potential C2 appearing at the ratio inverting input terminal of the operational amplifier U3 is e2=(R@+r)i
...-Q...■. The operational amplifier υ3 is e3-e2(1+(R2/R1))-el(R2/R
1) ” . . . 5). In equation (5), if R1-R2, then e3=2e2-el-(Rt
l-Ra)i---(
6) is obtained. Equation (6) is
Resistance value R of resistance temperature sensor PTI with respect to calculation reference resistance Ra
It shows the amount of change in tl and is not affected by the lead wires 11 and 12. This voltage e3 is applied to the operational amplifier u1 via the selection switch SWa, and then A
A/D conversion is performed, and the A/D conversion output is applied to an automatic balance circuit and measured.

Note that there are SWd and SWe as calculation reference resistance selection switches. This is done by switching the calculation reference resistances Ra and Rh, and thereby different types of resistance temperature detectors PTI...PTn
However, in this calculation reference resistance selection switch, either SWd or S'lle may be omitted.

〔Effect of the invention〕

The multi-point temperature measuring device of the present invention having such a configuration has the following effects.

(a) By providing a switch that disconnects all points of the resistance bulb from the internal circuit, the noise current flowing between the thermocouple and the resistance bulb is cut. As a result, in the device of the present invention, the error voltage Vnm due to noise can be made much smaller than in the conventional circuit shown in FIG.

The terminal to which the thermocouple is connected is a 3-point input terminal similar to the resistance temperature detector connection terminal, and the scanner switch is all a common scanner system that uses a 3-contact switching system, so both thermocouples and temperature measurement Not subject to restrictions on resistor terminal placement.

[Brief explanation of drawings]

FIG. 1 is a connection diagram showing an embodiment of a multi-point temperature measurement device according to the present invention, and FIG. 2 is a connection diagram of a conventional multi-point temperature measurement device. TC1~TCr+...Thermocouple, PTI~PTn...
Resistance temperature sensor A, B, b...input terminal, 5lfsl~S
'1lsn...Scanner switch, SWd...Calculation reference resistance selection switch, Ra...Calculation reference resistance, S
Wa to SWc...selection switch, υ1 to U3... operational amplifier.

Claims (1)

[Claims] Multi-point input terminals each having three terminals, two of which are connected to thermocouples or resistance temperature detectors, and the remaining one terminal commonly connected; each of which has three switching contacts; A scanner switch that scans the output of the thermocouple or resistance temperature sensor with two contacts, and a current source for the resistance temperature sensor is connected to the remaining one contact, and the thermocouple or resistance temperature sensor obtained through the scanner switch. a first selection switch for selecting the resistance temperature detector output; a first operational amplifier to which the thermocouple output is applied via the selection switch; a second operational amplifier that calculates and outputs a second operational amplifier; a second selection switch that applies the output of the second operational amplifier to the first operational amplifier when no thermocouple is selected by the first selection switch; A multi-point temperature measurement device comprising a calculation reference resistor connected to a common connection terminal in the input terminal via a reference resistance selection switch.