Elenco Electronics K-40, TA-12 Assembly And Instruction Manual
TEMPERATURE ADAPTER KIT
MODEL TA-12/K-40
Assembly and Instruction Manual
Elenco®Electronics, Inc.
ight © 2005, 1994 b
yr
Cop
t of this book shall be reproduced b
No par
y Elenco
®
Electronics
y means;
y an
, Inc.
electronic
ights reser
All r
, photocopying, or otherwise without written permission from the publisher.
ved. Revised 2005 REV-C 753125
PARTS LIST
If you are a student, and any parts are missing or damaged, please see instructor or bookstore.
If you purchased this kit from a distributor, catalog, etc., please contact Elenco
mail is at the back of this manual) for additional assistance, if needed. DO NOT contact your place of purchase
as they will not be able to help you.
RESISTORS
Qty. Symbol Description Color Code Part #
2 R5, R6 1kΩ 5% 1/4W brown-black-red-gold 141000
1 R7 3.3kΩ 5% 1/4W orange-orange-red-gold 143300
2 R1, R10 3.9kΩ 5% 1/4W orange-white-red-gold 143900
2 R4, R9 10kΩ 5% 1/4W brown-black-orange-gold 151000
1 R3 47kΩ 5% 1/4W yellow-violet-orange-gold 154700
2 R2, R8 10kΩ Trim Pot 191510
CAPACITORS
Qty. Symbol Description Part #
1 C1 .01µF, 50V (103) 241031
SEMICONDUCTORS
Qty. Symbol Description Part #
1 Q1 2N3904 NPN Transistor 323904
1 U1 LM1458N Op-Amp Integ
1 U2 MC7805 5V Regulator 337805
rated Circuit (IC) 331458
®
Electronics (address/phone/e-
MISCELLANEOUS
. Description Part #
Qty
1 PC Board
518040
1 Solder Roll 24” 551124
1 Battery Snap
1 IC Soc
ket 8-pin 664008
590098
1 Alligator Clip Black 680001
1 Alligator Clip Red 680002
1 Solid Black Wire 22ga. 6” 814120
1 Solid Red Wire 22ga. 6” 814220
Cable 2 Conductor 24” 876090
1
1 #7 Shrink Tubing 1/2” 890050
1 3/16” Dia. Shrink Tubing 1 1/2” 890120
PARTS IDENTIFICATION
Resistor Transistor
Capacitor
Regulator
Integrated
Circuit
IC Socket
8-pin
PC Board
Battery Snap
Trim Pot
-1-
Alligator Clip
Shrink
Tubing
3/16”
#7
INTRODUCTION
The TA-12/K-40 Temperature Adapter Kit is used in
c
onjunction with a digital multimeter to read
temperature. The Temperature Adapter consists of
THEORY OF OPERATION
VOLTAGE REGULATOR
The MC7805 (U2) is the voltage regulator which is
used to supply a constant voltage of about 5V to the
circuit.
TEMPERATURE SENSOR
The Temperature Sensor is an NPN transistor
(2N3904). The NPN transistor has three
terminals: the collector, base, and emitter as
shown in Figure 1. When the collector and base of
this transistor are shorted together as shown in
Figure 2, they behave exactly like a diode, which is
a temperature-sensitive device. At a constant
current, the voltage across the base to emitter
junction decreases by approximately 1mV for
every 1
O
F increase in temperature.
Collector
three main sections: • Voltage Regulator
•
Temperature Sensor
• Op-Amp
The op-amp senses the difference between the
voltage signals applied at its two terminals (that is,
the quantity v2 - v1), multiplies this by the open loop
gain A, and causes the resulting voltage A(v2 - v1)
to appear at output terminal 3 as shown in Figure 4.
In an ideal op-amp,
V+
the input impedance
is infinite, the output
impedance is zero
and the open loop
gain A is very large
and ideally infinite. In
, the open
actice
pr
loop gain is usually
greater than 100,000.
V1
i1 = 0
+
–
i2 = 0
+
V2
–
Figure 4
1
2
–
+
4
A(V2 - V1)
5
V–
3
Base
2N3904 NPN
Transistor
Base and
Emitter
Junction
Emitter
Figure 1
2N3904 NPN
Transistor
Figure 2
OP-AMP
The op-amp (LM1458) has tw
one output terminal. Figure 3 shows the op-amp
symbol. Terminals 1 and 2 are the input terminals,
and terminal 3 is the output
terminal. Many op-amps use
o DC po
tw
o terminals, 4 and 5, are
tw
connected to a positiv
wer supplies. The
e voltage
(V+) and negative voltage
(V–), respectively. The TA12/K-40 uses a single supply
with g
round tied to the
input.
o input terminals and
V+
1
2
V–
4
–
+
5
V–
Figure 3
3
In order to control the gain of our circuit we use
feedback to close the loop around the op-amp as
shown in Figure 5.
This circuit consists of an opamp and two resistors R1 and R2. Resistor R2 is
connected from the output terminal of the op-amp,
minal 3, back to the negative input ter
ter
minal,
terminal 1. We speak of R2 as applying negative
feedback; if R2 were connected between terminals
3 and 2, we would call this
positive feedback
. Note
that R2 closes the loop from the output terminal
k around to the input terminal of the op-amp. In
bac
this circuit, the closed loop gain (G) of the op-amp,
from the input Vi to the output terminal, depends on
the ratio of R2 to R1.
R2
1
+
Vi
R1
–
–
2
+
3
+
V0 = –(R2/R1) Vi
–
or
V0 = – GVi
Figure 5
For example, if R2 = 100 and R1 = 10, the gain G =
R2/R1 = 100/10 = 10. Thus, the output voltage V0
at terminal 3 would be equal to –10(Vi). The (–) sign
indicates that the output and input v
.
opposite polar
ity
oltages are of
-2-
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