®
®
DMS APPLICATION NOTE
Single-Component Thermometers
Introduction
The DMS-20 and DMS-30 Series of 3½ digit voltmeters are
ideal for constructing very accurate digital thermometers with only a
single external component — the LM34 or LM35 solid-state,
temperature-transducer IC's. The LM34 and LM35, both available
from National Semiconductor, are rugged three-terminal devices
designed to make temperature measurements in degrees Fahrenheit
or Celsius, respectively. They are both available in either TO-92
or TO-46 packages and cost approximately $2 (US) in
100-piece quantities.
The dc output voltage of both devices is linearly proportional to
their ambient temperature, i.e., at +77°F (+25°C), the LM34's output
is 0.77Vdc while the LM35's is 0.25Vdc. Neither device requires any
external calibration or trimming circuits to provide typical accuracies
of ±½°F (±¼°C) at room temperature and ±1½°F (±¾°C) over a full
–50 to +300°F (–55 to +150°C) operating temperature range.
However, although the LM34 and LM35 are specified to operate
below 32°F (0°C), the DMS Series meters have an operating
temperature range of 0 to +60°C (+32 to +140°F).
meter's specified operating temperature range. Care should be
taken when making connections to the LM34/35. The point at which
the wires attach to the LM34/35 should be kept at the same
temperature as the body of the LM34/35. This will ensure that the
connections themselves do not affect the overall measurement
accuracy by acting as heat sinks and drawing heat away from the
LM34/35's package.
Power Supply Requirements
Figure 1 shows the connections required for 5V-powered
meters, while Figure 2 shows the connections for 9V-powered LCD
meters. The input voltage range of all meters must be ±2 Volts
("-1" part number suffix). For 5V operation, any DMS-20, DMS-30 or
DMS-40 model — with LCD or LED displays — can be used with
either temperature sensor. For 9V operation, only the DMS-30LCD1-9 can be used, and only with the connections shown in Figure 2.
The 9V power source can either be a line-operated dc supply or a
battery. The power requirement for the LM34/35 is typically 70µA
while the DMS-30LCD-1-9 has a current drain of only 350µA.
External Connections
As previously noted, it is very important that any meter used
with the LM34/35 not be put into an environment that is outside the
+9V SUP
1
V+
LM35
+5V SUP
OUT
DMS-30LCD-1-9
8
11
(+) IN HI
REF OUT
12
1
V+
LM34
OUT
DMS-30PC-1-RL
11
(+) IN HI
GND
7
8
REF IN
REF OUT
2
DISP TST
12
GND
(–) IN LO
3
GND
4
DP3
(–) IN LO
7
REF IN
3
GND
4
DP3
Figure 2. LM35 Celsius Display Using DMS-30LCD-1-9
Figure 1. LM34 Fahrenheit Display Using DMS-30PC-1-RL
www.murata-ps.com
Technical enquiries email: [email protected], tel: +1 508 339 3000
DATEL, Inc., Mansfield, MA 02048 (USA) • Tel: (508)339-3000, (800)233-2765 Fax: (508)339-6356 • E-mail: [email protected] • Internet: www.datel.com
DATEL makes no representation that the use of its products in the circuits described herein, or the use of other technical information contained herein, will not infringe upon existing or future patent rights. The descriptions contained
herein do not imply the granting of licenses to make, use, or sell equipment constructed in accordance therewith. Specifications are subject to change without notice. The DATEL logo is a registered DATEL, Inc. trademark.