Conrad Digital Thermometer Module With LED Display Kit 192147 Data Sheet
Product codes
192147
However, since we are deriving here the voltage to be measured from the voltage divider
R7/ KTY10, there are only positive signals. We displace the zero point by artificially
laying “high” the measuring input 30 above the wiper of P2 (vis-à-vis the reference at 32
& 35).
R7/ KTY10, there are only positive signals. We displace the zero point by artificially
laying “high” the measuring input 30 above the wiper of P2 (vis-à-vis the reference at 32
& 35).
The IC rates everything that lies below the artificial reference level at pin 30 as minus-
signal and activates the negative sign. Since the voltage change at the temperature
sensor takes place below and above the reference level, positive and negative
measured values occur apparently. With reference to the connections 32 & 35 the
voltage at pin 31 continues to be only positive. As you see, it is only a matter of how you
look at it. We do the actual calibration of the scale through the setting of P1, which
defines the exact reference voltage at pin 36.
signal and activates the negative sign. Since the voltage change at the temperature
sensor takes place below and above the reference level, positive and negative
measured values occur apparently. With reference to the connections 32 & 35 the
voltage at pin 31 continues to be only positive. As you see, it is only a matter of how you
look at it. We do the actual calibration of the scale through the setting of P1, which
defines the exact reference voltage at pin 36.
Despite the good linearization a residual error continues to exist in the sensor
characteristic, which adds up to a little more than 2% with the tolerance in the pre-
resistor R7 (at the area boundaries). This is – with respect to the total effort – a very
good accuracy, the more so as the measurement error in the middle range approaches
almost zero (can be adjusted with the P1-setting).
characteristic, which adds up to a little more than 2% with the tolerance in the pre-
resistor R7 (at the area boundaries). This is – with respect to the total effort – a very
good accuracy, the more so as the measurement error in the middle range approaches
almost zero (can be adjusted with the P1-setting).
These considerations are crucial for the fact that there is no need to make an
exaggerated effort in case of critical components of the voltmeter (capacitors for the
zero-offset and the integrator) (standard types suffice). The deviations caused as a
result of this go down in system errors. On the other hand, metal-film resistors are to be
used for R5 and R7 and spindle potentiometers for P1 and P2.
exaggerated effort in case of critical components of the voltmeter (capacitors for the
zero-offset and the integrator) (standard types suffice). The deviations caused as a
result of this go down in system errors. On the other hand, metal-film resistors are to be
used for R5 and R7 and spindle potentiometers for P1 and P2.
Pay attention to the correct polarity in case of diodes and electrolytic capacitors: The
cathode-side (black ring) points away from IC1 in case of rectifier diode D2, away from
C2 in case of D1 and towards IC1/IC3 in case of D3. Contrary to the usual, the positive
pole is at the earth in case of electrolytic capacitor C1 (it buffers the negative auxiliary
voltage). Use those sockets for IC1 and IC3, whose marking notch can be aligned in the
same way as in IC, which these are supposed to accept; even the four displays use a
40-pin socket.
cathode-side (black ring) points away from IC1 in case of rectifier diode D2, away from
C2 in case of D1 and towards IC1/IC3 in case of D3. Contrary to the usual, the positive
pole is at the earth in case of electrolytic capacitor C1 (it buffers the negative auxiliary
voltage). Use those sockets for IC1 and IC3, whose marking notch can be aligned in the
same way as in IC, which these are supposed to accept; even the four displays use a
40-pin socket.
Most of the ICs have their contact pins spread towards outside, so that they do not fall
out again after an automatic mounting; however, they can be bent again towards one
another by applying a slight pressure against a surface.
out again after an automatic mounting; however, they can be bent again towards one
another by applying a slight pressure against a surface.
After mounting and a visual check for any soldering or mounting faults, you can carry out
two broad functional checks: Connect at bottom left a voltage of approx. 7…18 V and
measure at the right connection of IC3, whether +5 V (against earth) is present there. At
the anode of D2 (left) a voltage of approx. -4 V must be present (against earth), if
everything works well, and random values appear in the display.
two broad functional checks: Connect at bottom left a voltage of approx. 7…18 V and
measure at the right connection of IC3, whether +5 V (against earth) is present there. At
the anode of D2 (left) a voltage of approx. -4 V must be present (against earth), if
everything works well, and random values appear in the display.
Owing to the displaced zero point, the basic setting cannot be done in case of short-
circuit on the input side, but instead must be done at “real” zero degree Celsius. This can
be achieved very easily by filling a glass of water with ice (crushed cubes) for so long, till
the ice no longer melts even after stirring for a long time. In a saturated mixture of ice
and water a temperature of exact 0°C gets set, because each supply of heat (from the
environment) does not raise the temperature, but instead is used first for melting the
floating ice; only after that the temperature of water starts rising.
circuit on the input side, but instead must be done at “real” zero degree Celsius. This can
be achieved very easily by filling a glass of water with ice (crushed cubes) for so long, till
the ice no longer melts even after stirring for a long time. In a saturated mixture of ice
and water a temperature of exact 0°C gets set, because each supply of heat (from the
environment) does not raise the temperature, but instead is used first for melting the
floating ice; only after that the temperature of water starts rising.
Insert the sensor in a thin pipe and immerse both in the ice solution, in order to conduct
the zero offset with P2. Thereafter, look for a (plus-) reference temperature e.g. near the
huge thermometer of an optician’s shop, and set this reference with P1. the more exact
the zero offset with P2. Thereafter, look for a (plus-) reference temperature e.g. near the
huge thermometer of an optician’s shop, and set this reference with P1. the more exact