MEWOI MEWOI3800P User manual

Built-in Non-Contact Ground
Resistance Online Detector
MEWOI3800P

CONTENT
I. Brief Introduction ...........................................................................1
II. Technical Specifications................................................................2
III. Detector Structure and Dimensions .............................................4
IV. Usage method...............................................................................5
V. The Principle andApplication of Detection...................................6
VI. Basic Equipment........................................................................14

Attention Items:
Thank you for purchasing MEWOI3800P Built-in Non-Contact
Ground Resistance Online Detector of the company In order to
make better use of the product please be certain:
——To read this user manual carefully.
——To comply with the operating cautions presented in this
manual.
Apply to return circuit ground resistance, metallic return con-
nection resistance, grounding conditions, cable anti-theft
on-line monitoring.
Single point grounding system, needs to increase assistance
after the ends of the earth form a loop, then install detector.
Note that this detector specified measuring range and using the
environment.
Protection against rain shower and water logging of installation.
The detector and the circuit board can be built into other
equipment crate, which is convenient for integration.
Install waterproof and rainproof of device at outdoors.
The dismantling, calibration and maintenance the Detector shall
be operated by the authorized staff.
If the continuing use of it would be dangerous, the Detector
should be stopped using immediately, and immediately sealed
for the treatment by the authorized agencies.

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I. Brief Introduction
Built-in Non-Contact Grounding Resistance Online Detector is
our company devotes ourselves to Grounding resistance test tech-
nical research’s another new high-tech product for more than ten
years, built for online monitoring grounding down lead connection
status, return circuit grounding resistance and metal return circuit
connection resistance well-designed manufactured. on-line testing,
non-contact measurement, grounding wire pass through the hole,
real time on-line testing. Detector provides RS232 and RS485 signal
interface, provides standard MODBUS-RTU communication pro-
tocol. The detector and the circuit board can be built into other
equipment crate, which is convenient for secondary development
integration.
Non-Contact Grounding Resistance Online Detector is widely
applied in electric power, telecommunications, petrochemical, rail-
way, meteorology, military and other industries, building facilities,
electric power, electrical equipment, warehouse and oil depot of the
lightning protection grounding, protective grounding, or working
grounding, and also applied in anti-theft monitoring for ground wire
and metal cable.
Non-Contact Grounding Resistance Online Detector can be in-
dependent installation to use, and also can organizes a wire or wire-
less network system.

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II. Technical Specifications
Function
Return circuit grounding resistance on-line
monitoring, metal return resistance connection
online monitoring, grounding condition moni-
toring, ground wire and metal cable anti-theft
monitoring.
Power Supply
Detector: DC6V~ DC9V, 50ma Max.
Resistance
Range
0.01Ω~ 200Ω
Resolution
0.001Ω
Indication
Range
0.00Ω~ 200Ω
Accuracy
±2 % rdg±3dgt(20°C ±5°C , below 70%RH)
Detector Di-
mensions
110mm×80mm×55mm
PCB Dimen-
sions
166mm×56mm×20mm
Grounding
Wire Perfora-
tion Size
60mm×30mm, closed mode
Overflow Indi-
cation
When show value is beyond 200Ω, detector
send out “OLΩ”
PCB Interface
J1: signal output, power supply input interface
J2: Detector and PCB interface
J1 Identifier
P+: power supply input anode;
P-: power supply input cathode;
GND: signal cathode, connects with power
supply input cathode by short circuit connec-

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tion
R+: signal output anode
R-: signal output cathode
J2 Identifier
I+,I-: current coil interface
U+,U-: voltage coil interface
GND: common ground
Connecting
Line
A one meter long wire(5cores shielded wire)
Connection
Identifier
Red/brown---power supply input anode;
Black--- power supply input cathode;
Blue---RS485 signal anode;
Grey---RS485 signal cathode;
White--- analog grounding (power supply input
cathode can connects with analog grounding by
short circuit connection)
Protocol
Standard
RS232, RS485 or MODBUS-RTU communi-
cation protocol
Quality
Detector: 680g
Working Tem-
peratureAnd
Humidity
-20°C ~55°C ;20% RH~90% RH
Humiture Er-
ror
Within 5%
Shift
Automatic shift
GND Interfer-
ence Current
Prohibited
External Mag-
netic Field
< 40A/m

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External Elec-
tric Field
< 1V/m
Single Meas-
urement Of
Time
About 0.5 second
Power Con-
sumption
50ma Max.
Installation
Grounding wire through Detector centre bore
Installation
Requirements
The circuit board need built into other equip-
ment crate, avoid rain and water logging
Power Supply
Mode
External power supply (Equipped by user)
III. Detector Structure and Dimensions
1. Grounding wire perforation size: 66mm×36mm.
2. Detector.
3. Signal output, power supply input thread
4. Signal output and power supply input connecting wire.
5. Detector and PCB connecting wire.

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6. PCB.
IV. Usage method
1. Independent Installation and Use.
2. Set up Network Installation and Use
According to RS232, RS485 or MODBUS-RTU communication
protocol to set up a variety of networks to achieve remote monitor-
ing.

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V. The Principle and Application of Detection
1. Testing Principle.
Built-in Non-Contact Grounding Resistance Online Detector’s
fundamental is measuring return circuit resistance. firstly Sensor
send out a drive pulse signal to be measured ground return circuit,
then measured ground return circuit responses a pulse electromotive
force E, under the influence of electromotive force E there will gen-
erate current I in the be measured ground return circuit. Sensor
measures E and I, and immediately gets resistance of be measured
ground return circuit through the formula: R=E/I.
2. Return Circuit Resistance Definition.
As picture: return circuit is a composite value includes A spot
grounding resistance, grounding down lead metallic conductor’s
resistance, metal overhead line’s resistance, connection re-
sistance(contact resistance)between grounding down lead and metal
overhead line, B spot grounding resistance. For the formative
above-mentioned return circuit’s grounding system, Detector can be
installed directly for monitoring, if the grounding system not form a
return circuit, it need adding auxiliary grounding electrode to form a
return circuit, further install the Detector, see the after-mentioned
single point grounding system. If the Detector measured out return
circuit’s composite value of grounding network A and grounding
network B is 5.0Ω, that is: RA+RB+RC+ RD=5.0Ω(RC and RD re-
spectively represent resistance of metal overhead line and grounding
down lead ), actual grounding resistance value of grounding network
A and grounding network B’s in parallel resistances less than or
equal to 2.5Ω, accordingly judge actual grounding resistance value
of grounding network A and grounding network B parallel connec-

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tion whether qualified. If grounding network A and grounding net-
work B’s in parallel resistances less than engineering standard re-
quired value, so grounding network A and grounding network B are
all qualified.
3. Metal Return Circuit Connection Resistance Testing.
If grounding network A and grounding network B up and down are
connected together on the ground, then Detector measures out metal
return circuit resistance’s value is very small general speaking, only
few of an Ohm, this is the connection resistance of metal return cir-
cuit, namely equipotential resistance, isn’t grounding resistance.
Therefore the Detector is convenient to test metal return circuit’s
connection resistance, and also applied in anti-theft monitoring for
ground wire and metal cable.When the cable is cut, metal loop re-
sistance is infinite, the Detector will alarm.
In the large-scale grounding grid, such as converting station ground
connection, oil depot ground connection, building construction

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ground connection and so on, they are all an integral large-scale
grounding grid under the ground, meanwhile there are many
grounding down lead extends to the ground, and connects the other
on the ground, as the following picture. To such large-scale ground-
ing grid, its grounding grid’s maximum diagonal distance is about a
few hundred meters to thousands of meters, testing its grounding
resistance is very difficult and troublesome. If it exist unqualified
grounding resistance, that problem is appearing at the connection
position of grounding down lead and grounding grid (direction of
arrow of the welding position in the picture), engineering reform is
to excavate grounding down lead’s position, then again weld
grounding down lead. Actually it’s impossible to reform the whole
grounding grid, or the whole grounding grid and surface facilities
need to pull down and rebuild, this is impossible.
Therefore, for the large-scale grounding grid, we can install Detector
on the primary grounding down lead and secondary grounding down
lead to monitor connection status between the grounding down lead
and the grounding grid, judge the grounding down lead’s grounding
conditions by testing metal return circuit connection resistance.

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4. Single Point Grounding System.
If grounding network A and grounding network B is without over-
head line, and doesn’t connect together on the ground, then ground-
ing network A and grounding network B can regard as standalone
single point grounding connection. Detector cannot test single point
grounding system’s grounding resistance directly. This moment it
needs adding one or more auxiliary grounding electrode, to form
multipoint return circuit, then to install Detector. In the small range,
if there are two or more single point grounding system, it can use
metallic conductor to connect all single point grounding system’s
grounding down lead together on the ground, to form a return circuit,
then install the Detector to monitor.
5. Three-point method
As figure, A is the tested ground pole, B and C are auxiliary ground
poles. Ground pole A, B and C are connect together on the ground.
In the grounding down lead of the three ground pole A, B and C,
install the Detector respectively, can accurately test the grounding
resistance ofA point. Calculation is as follows:
R1=RA+RB∥RC--------(1);
R2=RB+RA∥RC--------(2);
R3=RC+RA∥RB--------(3).
Illustration: R1, R2, R3 are the test values, RA, RB, RC are the
grounding resistance of the ground pole A, B and C. By solve the
three equations, can be accurate calculate the grounding resistance of
ground pole A, at the same time, it can know the grounding re-
sistance of auxiliary ground pole B,C and the grounding resistance
of parallel connectionA, B and C.

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Three-point method has another advantage: Due to auxiliary ground
pole B and C is parallel to the tested ground pole A, so that the actu-
al grounding resistance will be less than RA to improve the tested
grounding pole. RA∥RB∥RC＜RA. At the actual construction, the
grounding resistance of auxiliary ground pole B and C must less
than 10 times of the grounding systems engineering standard value.
If the engineering requirements of the grounding resistance value
cannot exceed 4Ω,then RC＜40Ω,RB＜40Ω. RB, RC as small as
possible, more can improve measured grounding system.
6. Application.
(1). Power Transmission System Pole Ground Connection.
It forms multipoint grounding system through overhead ground wire
connection; test conveniently, its equivalent circuit as the following
picture on the right.

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Illustration:R1 is predicted grounding resistance, R0 is the equiva-
lent resistance of all the other pole’s grounding resistance parallel
connection, that is R0=R2∥R3∥R4∥…∥Rn, if the greater n is (the
more grounded junction), the closer R0gets to 0,far smaller than R1,
from engineering point of view, R0=0,so, the data Detector receives
should be R1’s value.
(2). Underground Mine Power Transformation Ground Connection.
Respectively, primary grounding electrode R,R1～R3…Rnis a inde-
pendent grounding body under the ground, don’t connect together,
are multipoint grounding system, convenient to test. Detector is in-
stalled on the primary grounding electrode, the Detector’s indication
is Rr=R+R1∥R2∥R3∥…∥Rn. If the more part grounded junctions
are, so R1∥R2∥R3∥…∥Rn≈0,then Rr=R. It’s the four-code cable
in the picture, one code is ground lead among it, all the devices and
part grounding connection are connected to be a network by cable
grounding connection, dotted line is bare copper wire of grounding
connection.

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(3). Generator Room and Launch Tower Grounding Connection.
Generator Room and Launch Tower is independent outdoors gener-
ally, connect both together to form second return circuit, then install
detector, as the picture below. It also can add 2 auxiliary ground
poles, use the three-point method to monitor.

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(4). Construction Grounding Connection.
If R1～R6…Rnis a independent grounding body under the ground,
don’t connect together, are multipoint grounding system, convenient
to test grounding resistance. If R1～R6…Rnare connected together
under the ground, for the single point grounding system, testing
grounding resistance in accordance with single point grounding sys-
tem, direct installation test return circuit resistance, can judge
grounding connection condition.
For the large-scale construction grounding grid, it is to monitor its
equipotential value of grounding condition between grounding down
lead and grounding network. If problems occur, it would be located
at the connection point between grounding down lead and ground-
ing network, and judging that whether its equipotential value quali-
fied or not.

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(5).Oil Storage Tank’s loading and Unloading Point Grounding
Connection.
Base on JJF2-2003<<Grounding Type Antistatic Device Test Speci-
fication>>, gas station mainly need to test the grounding resistance
and connect resistance of the facility shows below.
No.
Item
Technical Speci-
fication
1
Grounding resistance of oil storage
tank
≤10Ω
2
Grounding resistance of load or unload
place
≤10Ω
3
Grounding resistance of Fuel dis-
penser
≤4Ω
4
Resistance of oil hose which connect
to the Fuel dispenser and fuel truck
nozzle
≤5Ω
VI. Basic Equipment
Detector
1Set

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PCB module
1PCS
Connecting wire
1 Set
User's Manual, Warranty Manual, Certification
1 Set

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