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參數(shù)資料
| 型號： | ELM331SM |
| 廠商： | Electronic Theatre Controls, Inc. |
| 英文描述： | Solid State Thermostat |
| 中文描述： | 固態(tài)溫控器 |
| 文件頁數(shù)： | 4/4頁 |
| 文件大小： | 28K |
| 代理商： | ELM331SM |
Example Application
4 of 4
Figure 1. Backup Heating Control Thermostat
Figure 1 shows the ELM331 in an example heating
control circuit. A closed contact output occurs
whenever the temperature measured by R
TEMP
falls to
a value less than that determined by R
SET
. It is
anticipated that this type of circuit could possibly be
used to control temperatures over the range of -40°C
to +40°C.
Power for the circuit is from a 12V supply, that is
reduced to 5V by the 78L05 regulator. This gives a
stable supply voltage for the ELM331, as well as
convenient voltage for use with a standard relay coil.
The type of relay is not important, as long as
consideration is given to its coil requirements, and the
capabilities of the ELM331. In this example, a relay
with a 400
coil resistance was chosen so that a
2N3904 could drive it directly.
Temperature measuring is performed by R
TEMP
,
which is a negative temperature coefficient type
thermistor. It has a resistance of 10K
at 25°C, and
this value decreases with increasing temperature. This
value was chosen both because it is commonly
available, and because it limits the 0.1μF integrating
capacitor currents to less than 1mA over the typical
range of operation (keeping the thermistor self-heating
to a minimum).
If the thermistor is mounted any appreciable
distance from the ELM331, consideration must be
given to cabling effects such as capacitive and induced
currents. Generally the integrated circuit can be
adequately protected by mounting a small value (220
)
resistor physically close to the ELM331 as shown
below. Take into account it’s value when determining
the setpoint, though.
For this design, R
SET
was selected to be equal to
the resistance of R
TEMP
at 10°C, so that the relay
contact closes for any measured temperatures less
than 10°C. The resistance value was determined from
specs given by the manufacturer, but could have been
determined experimentally as well.
An LED has been provided for visual feedback of
the circuit operation. It is connected to the
‘measurement in progress’ output, so that it is
energized each time a measurement is being made.
Typically, this would be for about 25mS every 2
seconds.
Variations on this circuit could easily be made…
Simply by reversing R
SET
and R
TEMP
, one obtains a
cooling control thermostat… Rather than a relay output,
the circuit could have been connected directly to other
logic circuits. The measurement in progress pin could
then be used either as an interrupt, or as a busy flag
that can clock in new results on it’s falling edge…
Battery backup is another option that could be
added to this circuit, but then consideration should be
given to using the ELM341 Low Power Thermostat…
ELM331
ELM331DSB
< http://www.elmelectronics.com/ >2.2K
560
10K
R
SET
18K
R
TEMP
10K
@25°C
0.1μF
78L05
2N3904
LED
1N4001
To the
heating
control
0.1μF
+12V
+12V
0.1μF
1
2
3
4
8
7
6
5
12V Relay
see text
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| ELM331DSB | Solid State Thermostat |
| ELM334 | GARAGE DOORMAN |
| ELM334P | GARAGE DOORMAN |
| ELM334SM | GARAGE DOORMAN |
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