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DMS APPLICATION NOTE
Selecting 1% Resistors
Introduction
Many of the application notes in this section make reference to,
or specify the use of, ±1% metal-film resistors. The table below lists
all readily available, E-96 series, 1% resistor values. Please see the
component suppliers index for the name and address of 1% resistor
suppliers.
Using the Table
Using the table is straightforward. First determine the required
value. Then, using just the first three digits of the required value, find
the closest number to the three digits in the table — disregard the
decimal points for this step. For example, your calculations indicate
that a 1,342Ω resistor is needed for an input-scaling circuit. The first
three digits are "134". The closest value to 134 in the table is "13.3".
Multiply 13.3 by 100. The result, 1,330Ω, is the closest commercially-available resistor value, commonly referred to as 1.33kΩ .
The total number of resistors available is not infinite; most
manufacturers stock values from 10Ω through 10,000,000Ω (10
Megohm). This means you can apply multipliers of 1 (10 0) through
1,000,000 (10 6) to the numbers in the table. The most common
wattage ratings are 1/8 and 1/4 Watt; though 1/2 and 1 Watt units
are also available. Values above 1 Megohm are usually more
available in ratings of 1/4 Watt or higher.
Voltage Rating
Two other resistor parameters to be aware of are working
voltage and temperature coefficient of resistance (TCR). Most
1/4-Watt resistors are rated for 200V continuous operation. 1/2 Watt
E-96 (±1%) Decade Values Table
10.0
10.2
10.5
10.7
11.0
11.3
11.5
11.8
12.1
12.4
12.7
13.0
13.3
13.7
14.0
14.3
14.7
15.0
15.4
15.8
16.2
16.5
16.9
17.4
17.8
18.2
18.7
19.1
19.6
20.0
20.5
21.0
21.5
22.1
22.6
23.2
23.7
24.3
24.9
25.5
26.1
26.7
27.4
28.0
28.7
29.4
30.1
30.9
31.6
32.4
33.2
34.0
34.8
35.7
36.5
37.4
38.3
39.2
40.2
41.2
42.2
43.2
44.2
45.3
46.4
47.5
48.7
49.9
51.1
52.3
53.6
54.9
56.2
57.6
59.0
60.4
61.9
63.4
64.9
66.5
68.1
69.8
71.5
73.2
75.0
76.8
78.7
80.6
82.5
84.5
86.6
88.7
90.9
93.1
95.3
97.6
and higher types can be obtained with ratings in excess of 500V.
Resistor voltage ratings are a very important consideration when
designing dividers with input voltages greater than 200Vdc or
120Vac. A safety-minded point to keep in mind when designing any
type of input divider is to always use resistor values that add up to
at least 1 Megohm. Doing so will generally allow the use of readily
available 1/4-Watt resistors.
Temperature Coefficient
Applications using 3½ digit meters (DMS-30 and DMS-20) can
use resistors with TCR's of 50 to 100ppm. TCR is normally specified
in ppm/°C (parts per million per degree Centigrade). 4½ digit meters
should use 25ppm, or better, resistors. To put this into terminology
that is more easily understood, one count ("001") on the display of a
DMS-20 meter is 500ppm. One count ("0001") on a DMS-40 meter
is 50ppm!
As a worst-case example, assume two ±100ppm resistors are
used in a ten-to-one input divider for a DMS-40PC and the ambient
temperature goes up by 2°C. If one resistor has a TCR of +100ppm
and the other has a TCR of -100ppm, a total change of 200ppm/°C
x 2°C = 400ppm would occur. Since one count on the display is
50ppm, the meter's reading would change by 400/50 = 8 counts.
In some applications, 8 counts may be a very significant change!
Color
Black
Brown
Red
Orange
Yellow
Green
Blue
Violet
Gray
White
Gold
www.murata-ps.com
Band 1
0
1
2
3
4
5
6
7
8
9
Band 2
0
1
2
3
4
5
6
7
8
9
Band 3
0
1
2
3
4
5
6
7
8
9
Band 4
10 0
10 1
10 2
10 3
10 4
10 5
10 6
10 7
10 8
10 9
10 -1
Band 1
Band 5
Band 2
Band 4
Band 5
±1%
±0.5%
±0.25%
±0.1%
Band 3
To measure input voltages
greater than ±100Vdc,
open SG10 and also cut
these two etch paths.
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