Introduction
The question of how the performance of DMS-Series meters is affected
when they are subjected to ambient temperatures outside their specifi ed
operating range is one we frequently encounter. The answer to this question
depends on which display technology the meter employs: either LED (Light
Emitting Diode) or LCD (Liquid Crystal Display). As shown in the table on
page 2, within the limits specifi ed later in this application note, the meter's
A/D converter, reference circuit, and passive components are not adversely
affected by temperature extremes. However, for reasons described below,
LED display meters are better suited for extended temperature operation.
DMS-Series meters' operating temperature ranges of 0 to +60C for 3
digit meters and 0 to +50C for 4 digit meters are more than adequate for
the majority of panel meter and process monitoring applications. (These two
ranges are widely regarded as industry standards.) Unless otherwise noted
on individual product data sheets, DATEL guarantees its panel meters and
process monitors to meet all published specifi cations over the applicable 0 to
+50C or 0 to +60C operating temperature range.
DATEL performs all standard production testing of its panel meters at
25C room temperature. Our general purpose, 12-pin DIP, DMS-20PC/LCD
and DMS-30PC/LCD meters receive sample-testing at +60C, with accuracy,
stability, and zero reading being the parameters of interest.
For purposes of specifi cation guard-banding, DATEL also performs rou-
tine QA-qualifi cation and engineering tests at temperatures well above and
below the ranges specifi ed on our data sheets. The table on page 2 shows
actual display readings of nine LED display DMS-Series meters taken at eight
different operating temperatures. Using a near full-scale positive input, each
meter was initially calibrated at +25C to an accuracy of 1 count ("least
signifi cant digit"). All meters were subjected to a 30-minute soak time at each
temperature before the readings were taken.
LCD Display Meters
The displays used in DMS-20LCD, DMS-30LCD, and DMS-40LCD series
meters, including all process monitors and 2-wire meters with `LCD' in their
part numbers, employ a liquid-crystal fl uid sandwiched between two layers
of glass, with the two layers of glass glued together. The liquid-crystal fl uid
physically moves as information to the display is updated.
At temperatures below 0C, the fl uid's movement becomes more slug-
gish. This sluggishness causes the interval required for the display to change
from one reading to another to become progressively longer; from hun-
dredths of a second at +25C, to tenths of a second at 0C. The end result
is a diffi cult-to-read display that suffers from a phenomenon referred to as
"ghosting," that is, old information and new information are simultaneously
displayed.
At temperatures above +70C, commercial LCD displays begin to turn
black, a condition which renders them unreadable. Also, because of the
nature of the display's construction, LCD-based meters are not physically able
to tolerate environmental extremes, and therefore are not recommended for
operation outside their specifi ed temperature ranges.
LED Display Meters
Due to the fact that the light-emitting elements used in DATEL LED-
display meters are solid-state semiconductors, they exhibit excellent electrical
and mechanical characteristics over very wide temperature ranges. As such,
their operational temperature limits are to a large extent dependent on the
plastic packaging materials that house them. Therefore, DATEL's LED-display
digital panel meters are the best choice when extended operating tempera-
ture, overall ruggedness, and long-term reliability are paramount concerns.
The most noticeable effect extended temperatures have on our LED
meters' performance pertains to display brightness. At 40C, the LED display
becomes noticeably brighter, while above +60C the display becomes notice-
ably dimmer, though still easily readable. This varying intensity is due to
an electro-optical characteristic exhibited by practically all LEDs: conversion
effi ciencies increase as temperature is lowered, and decrease as temperature
is raised from +25C. However, because our segment drive-currents remain
relatively constant with varying temperature, the meter's total power dissipa-
tion also stays constant.
Conclusion
Results from qualifi cation and engineering tests (see page 2) allow
DATEL to conditionally state that LED display DMS-20PC, DMS-30PC, and
DMS-40PC standard- and high-intensity models (`-RS' and `-RH' part number
suffi xes, respectively) will remain fully operational at operating temperatures
of 40C to +70C. Low-power models (`-RL', and `-GL' suffi xes) of these
same three families can be briefl y exposed to operating temperatures of up to
+80C. However, only the operating range specifi ed on product data sheets --
either 0 to +50C for 4 digit meters or +60C for 3 digit meters -- is guar-
anteed. Also, keep in mind that continuous exposure to elevated temperatures
will have a negative impact on any electronic device's long-term reliability.
The above information regarding extended temperature operation is
intended to serve as a guide. Real-world applications often include issues that
have not been considered or discussed in this application note. Please consult
DATEL if you have any questions regarding your specifi c application.
Related Documents
DMS Application Note 1: "The LED versus LCD Decision"
DMS Application Note 19: "Half-Digits, Resolution and Other
DPM Display FAQ's"
Quality Assurance Link: http://www.datel.com/qa_dpm.htm
Extended Temperature Operation
of DMS-Series Meters
DATEL, Inc.
, Mansfi eld, MA 02048 (USA)
Tel: (508)339-3000, (800)233-2765 Fax: (508)339-6356
Email: sales@datel.com
Internet: www.datel.com
DMS APPLICATION NOTE
Model Number
Input Voltage
40C 25C 0C +25C +50C +60C +70C +80C
DMS-20PC-0-RS
190.0mV 189.7 189.8 189.8 189.8 190.1 189.9 189.9 189.8
100.0mV 99.8 99.9 99.9 99.9
100.1 99.9 100.0
100.0
0mV 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0
+50.0mV 49.9 50.0 50.0 50.0 50.1 50.0 50.1 50.1
+100.0mV 99.8 100.0 100.0 100.0 100.1 100.0 100.1 100.1
+190.0mV 189.8 189.9 189.9 189.9 190.0 189.8 189.9 190.0
DMS-20PC-1-RL
1.900V 1.899 1.900 1.899 1.899 1.901 1.900 1.900 1.900
1.000V 1.000 1.000 1.000 .999 1.001 1.000 1.000 1.001
0V .000 .000 .000 .000 .000 .000 .000 .000
+0.500V .500 .500 .500 .500 .501 .500 .500 .501
+1.000V 1.000 1.000 1.000 1.000 1.001 1.000 1.001 1.001
+1.900V 1.900 1.900 1.900 1.899 1.901 1.900 1.901 1.901
DMS-20PC-2-GS
19.00V 19.03 19.02 19.01 18.99 19.01 19.00 19.00 18.92
10.00V 10.00 10.01 10.01 9.99 10.01 10.00 10.00 9.96
0V 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
+5.00V 5.01 5.01 5.00 5.00 5.00 5.00 5.00 4.98
+10.00V 10.02 10.01 10.01 10.00 10.01 10.00 10.00 9.96
+19.00V 19.04 19.02 19.01 18.99 19.01 19.00 19.00 18.93
DMS-30PC-0-RL
190.0mV 190.1 190.0 189.9 189.9 189.8 189.6 189.6 189.5
100.0mV 100.0 100.0 100.0 99.9 100.0 99.8 100.0 99.8
0mV 00.0 00.0 00.0 00.0 00.0 00.0 00.0 00.0
+50.0mV 50.0 50.0 50.0 50.0 50.0 49.9 50.0 50.0
+100.0mV 100.0 100.0 100.0 100.0 99.9 99.8 100.1 99.9
+190.0mV 190.2 190.0 190.0 190.0 189.8 189.6 189.6 189.6
DMS-30PC-1-RS
1.900V 1.899 1.899 1.899 1.898 1.901 1.900 1.900 1.900
1.000V 1.000 1.000 1.000 .999 1.001 1.000 1.000 1.000
0V .000 .000 .000 .000 .000 .000 .000 .000
+0.500V .500 .500 .500 .500 .500 .500 .500 .501
+1.000V 1.000 1.000 1.000 1.000 1.001 1.000 1.000 1.002
+1.900V 1.900 1.900 1.900 1.899 1.902 1.901 1.902 1.903
DMS-30PC-2-BS
19.00V 19.00 18.99 18.99 18.99 19.00 19.00 19.01 19.01
10.00V 10.01 10.00 10.00 10.00 10.01 10.01 10.01 10.01
0V 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00
+5.00V 5.01 5.00 5.00 5.00 5.01 5.01 5.01 5.01
+10.00V 10.01 10.00 10.00 10.00 10.01 10.01 10.01 10.02
+19.00V 19.01 19.00 19.00 19.00 19.01 19.01 19.02 19.04
DMS-40PC-1-RL
1.9000V 1.8947 1.8972 1.8985 1.8999 1.9006 1.9007 1.9006 1.9001
1.0000V .9974 .9987 .9994 .9999 1.0005 1.0000 1.0004 1.0002
0V .0000 .0000 .0000 .0000 .0001 .0001 .0001 .0001
+0.5000V .4986 .4994 .4997 .5000 .5003 .5003 .5003 .5003
+1.0000V .9974 .9986 .9993 1.0000 1.0004 1.0001 1.0004 1.0003
+1.9000V 1.8946 1.8973 1.8985 1.9000 1.9006 1.9007 1.9006 1.8976
DMS-40PC-1-RS
1.9000V 1.8962 1.8983 1.8991 1.8999 1.9000 -1.8997 1.8992 1.8976
1.0000V .9983 .9992 .9997 .9999
1.0002 -1.0000 .9998 .9992
0V .0000 .0000 .0000 .0000 .0001 .0001 .0001 .0001
+0.5000V .4990 .4996 .4999 .5000 .5001 .5000 .5000 .4998
+1.0000V .9982 .9992 .9996 1.0000
1.0001
1.0000 .9998 .9992
+1.9000V 1.8962 1.8984 1.8992 1.9000 1.8999 1.8997 1.8992 1.8976
DMS-40PC-2-RS
19.000V 19.014 19.009 19.006 18.999 18.973 18.963 18.955 18.943
10.000V 10.012 10.008
10.005 9.999 9.987 9.982 9.977 9.972
0V 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
+5.000V 5.006 5.004 5.002 5.000 4.994 4.991 4.989 4.986
+10.000V 10.012 10.008
10.005 10.000 9.987 9.982 9.977 9.972
+19.000V 19.015 19.010 19.007 19.000 18.973 18.963 18.955 18.944
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. Specifi cations are subject to change without notice. The DATEL logo is a registered DATEL, Inc. trademark.
The table below shows the actual display readings of nine LED-display
DMS-Series meters when they were operated at the indicated temperatures.
The models chosen are all +5V-powered and include the three most poplar
input ranges: 200mV, 2V, and 20V. All meters were initially calibrated
Extended Temperature Performance Table
at +25C with a single-ended, near full-scale, positive input to an accuracy
of 1 count (shaded readings under the +25C column). The readings
were recorded after a 30 minute "soak" period to ensure uniform internal
temperatures.
= Indicates initial calibration point of +
25C 3
DMS APPLICATION NOTE 22
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