Tinker&Rasor SR-2 - Page 3

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CORROSION MITIGATION INSTRUMENTATION
P. O. BOX 1667 SAN BERNARDINO, CA 92402 TEL: (909) 890-0700 FAX: (909) 890-0736
PRODUCT INSTRUCTIONS
MODEL SR-2 SOIL RESISTIVITY METER
The Test Indicator LED just above the PUSH TEST button will light during testing. If this LED is
blinking, the battery is low and will need to be charged within 24 hours. (See CHARGING below.)
If the LCD display shows “1_ _ _.”, move the RANGE SELECTOR switch one position clockwise (right),
and hold the PUSH TEST button down for 3 seconds. Repeat this procedure, moving the RANGE
SELECTOR switch one position clockwise each time, and holding the PUSH TEST button down for 3
seconds at each position.
When the LCD display shows an actual number, meaning the display changes from 1_ _ _. to something
like 3.9 or other, this is the result of the resistance of the soil. Do not move the RANGE SELECTOR
switch any further.
Make note of the number displayed on the LCD meter.
The Wenner 4-PIN Method describes a formula to be used to convert these results into Ohm-cm. This
formula is found in the ASTM G57-95(a) standard, as well as the Peabody’s Control of Pipeline
Corrosion,2
nd
Ed., pg. 87.
FORMULA:
The table below shows common distances and the multipliers to use for them.
COLUMN A
COLUMN B
PIN
SEPARATION (m)
MULTIPLIER
PIN
SEPARATION (m)
MULTIPLIER
RESULT
5 ft. (1.52m)
957.5
5.2 ft. (1.58m)
1000
(Range Selector) x (Display)
10 ft. (3.05m)
1915
10.4 ft. (3.17m)
2000
(Range Selector) x (Display)
15 ft. (4.57m)
2872.5
15.7 ft. (4.79m)
3000
(Range Selector) x (Display)
20 ft. (6.10m)
3830
20.9 ft. (6.37m)
4000
(Range Selector) x (Display)
25 ft. (7.62m)
4787.5
26.1 ft (7.96m)
5000
(Range Selector) x (Display)
NOTE: The middle column shows pin separations that are uncommon, but make the math much
easier, as the multipliers are round numbers.
SAMPLE EQUATIONS:
Example Formula COLUMN A:
Using 5 ft. Pin Separation
Meter shows 37.9
Range Selector Switch
is in Ohm range (x1)
(957.5) x (1) x (37.9) = 36,289.25 Ohm-cm
or 36.289 K ohm-cm
Example Formula COLUMN B:
Using 10.4 ft. Pin Separation
Meter shows 0.39
Range Selector Switch
is in KOhm range (x1,000)
(2000) x (1000) x (0.39) = 780,000 Ohm-cm
or 780K Ohm-cm
FORMULA:
ρ, Ω x cm = 2 π a R (a in cm) = 191.5 a R (a in ft)
R = average resistivity