Tegam R1M-A, R1M-AR Operation And Maintenance Manual

Revised August, 2004

10 TEGAM WAY • GENEVA, OHIO 44041 • 440-466-6100 • FAX [phone]

• [e-mail]

R1M-A, R1M-AR

MEGOHMMETER

MODEL R1M-A, R1M-AR

Operation and Maintenance Manual

PN# R1M-A-900-01

Publication Date: December 2012

REV. C

REPRODUCTION AND DISTRIBUTION OF THIS TECHNICAL MANUAL IS AUTHORIZED FOR US

GOVERNMENT PURPOSES. TEGAM PROPRIETARY INFORMATION.

NOTE: This User’s Manual was as current as possible when this product was manufactured. However,
products are constantly being updated and improved. To ensure you have the latest documentation, refer
to www.tegam.com

Revised August, 2004

10 TEGAM WAY • GENEVA, OHIO 44041 • 440-466-6100 • FAX [phone]

• [e-mail]

TABLE OF CONTENTS

TABLE OF CONTENTS

1. INSTRUMENT DESCRIPTION

Purpose ........................................................................ 1-1

Performance Characteristics ............................................ 1-1

Description of Equipment ................................................ 1-2

List of Items Furnished ................................................... 1-3

Storage and Shipping Requirements ................................. 1-3

2. PREPARATION FOR USE AND INSTALLATION

Unpacking and Inspection ............................................... 2-1

Preparation for Use ........................................................ 2-1

Figure 1: Connection Diagram ..................................... 2-3

3. OPERATING INSTRUCTIONS

Pushbutton Functions ..................................................... 3-1

General Theory of Operation ........................................... 3-2

4. PRINCIPLES OF OPERATION

5. MAINTENANCE

Inspection ..................................................................... 5-1

Cleaning ....................................................................... 5-1

Test Equipment required for Calibration and Repair ............ 5-1

Performance Verification ................................................. 5-2

Calibration .................................................................... 5-3

Troubleshooting ............................................................. 5-4

Table 2: Fault Symptoms and Repair Actions ................. 5-5

Preparation for Shipment ................................................ 5-6

Overhaul Instructions ..................................................... 5-6

Figure 2: Front Panel Controls ..................................... 5-7

Figure 3: Front Panel-Rear View .................................. 5-8

Figure 4: Simplified Block Diagram .............................. 5-9

Figure 5: Power Supply Schematic ............................. 5-10

Figure 6: Power Supply Layout .................................. 5-11

Figure 7a, 7b: Display Board Schematic ...................... 5-12

Figure 8: Display Board Parts Layout .......................... 5-14

Figure 9: System (Side View) Layout ......................... 5-15

Table 3, 4, 5, 6: Parts List ........................................ 5-16

Table 7: Vendor Cage Code Directory ......................... 5-19

6. SERVICE INFORMATION

Preparation for Repair or Calibration Service ..................... 6-1

Expedite Repair and Calibration Form ............................... 6-2

Warranty ...................................................................... 6-3

Revised August, 2004

10 TEGAM WAY • GENEVA, OHIO 44041 • 440-466-6100 • FAX [phone]

• [e-mail]

1-1

INSTRUMENT DESCRIPTION

SECTION 1

INSTRUMENT DESCRIPTION

INTRODUCTION

1.1 Purpose

The Model RIM-A Megohmmeter is a portable instrument used
to measure high values of resistance. It is enclosed in a
rugged weather-resistant housing designed for severe
industrial and military applications.
The Model RIM-A may be used to measure resistances
between 50 kΩ and 10 GΩ with 50 V test voltage, and
between 1 MΩ and 200 GΩ with 100 V, 250 V, or 500 V test
voltage.

1.2 Performance Characteristics

This is a digital reading instrument with six resistance ranges
and four test voltage ranges.

Range

Full Scale

(Ω)

Resolution

(Ω)

Test Voltage

(V)

1

1 M

1 k

50

2 10 M

10 k

100,
250,

or 500

3

100 M

100 k

4

1 G

1 M

5

10 G

10 M

6

100 G

100 M

Table 1: Specifications

Accuracy:
Resistance accuracy on all ranges: ± 5%
Test Voltage accuracy on all ranges: ± 3%

Revised August, 2004

10 TEGAM WAY • GENEVA, OHIO 44041 • 440-466-6100 • FAX [phone]

• [e-mail]

1-2

INSTRUMENT DESCRIPTION

1.3 Description of Equipment

Physical: A rugged heavy-duty case is provided to contain
and protect the instrument. When closed, a gasket seals the
lid to protect the instrument against water and dirt while the
instrument is carried through rainstorms or other hazardous
conditions. The lid is secured by two latches. A handle is
provided for portability. A compartment is provided for
storage of test cables and line cord.

Dimensions: 216 mm (8.5”) x 228 mm (9”) x 152 mm (6”).
Weight is 2.3 kg (5 lb). Controls and connectors are of a size
and spacing such that the instrument may be operated while
wearing safety gloves.

Electrical: Input power is from the AC power line (103.5 V to

129 V at 50 Hz or 60 Hz, at less than 1/8 A).

Environmental: This unit will operate over a temperature
range from 0 °C to 50 °C, 75% RH non-condensing, up to
3050 m altitude. Withstand functional shock of 40 G for 11
ms. Vibration: 2 G maximum at 5 Hz to 55 Hz.

Front Panel Controls and Displays (See figure 2)

OHMS RANGE Switch is a rotary six position selector switch

used to step through all six ranges.

TEST VOLTAGE RANGE Switch is a rotary four position selector

switch used to step through all four voltage ranges.

POWER Switch is used to turn the power on or off to the

instrument.

TEST pushbutton is a round sealed switch. This pushbutton

switch turns on the power to the unit. A LED is provided to
indicate that the test voltage is on.

DISPLAY is a 3 ½ digit LCD, displaying readings from 1.999

to 199.9.

Revised August, 2004

10 TEGAM WAY • GENEVA, OHIO 44041 • 440-466-6100 • FAX [phone]

• [e-mail]

1-3

INSTRUMENT DESCRIPTION

TEST VOLTAGE Jack is recessed to prevent any accidental

encounter.

Three Binding Posts for connection of test leads are marked

SIG (Signal), GUARD and GND (Ground). Proper connections
to the resistor under test are described in Section 2.2 below.

WARNING

DO NOT TOUCH THE BINDING POSTS WHEN THEY ARE
CONNECTED TO EXTERNAL CIRCUITS. LETHAL
VOLTAGES MAY BE PRESENT AT THESE POSTS.

1.4 List of Items Furnished

1 each Model R1M-A with power cord
2 each test cables, one shielded with two alligator clips

and the other with one alligator clip

1 each R1M-A Instruction Manual

1.5 Storage and Shipping Requirements

Standard precautions which apply to electronic test
instruments should be followed. A hard mechanical
shock, such as from dropping the R1M-A, could damage
the liquid crystal display. Care should be taken to
prevent damage to associated cables.

The R1M-A should be stored in a relatively dust-free
environment.
Temperature: -40 °C to +71 °C.
Relative humidity: 0 to 100%, non-condensing.
Altitude: 4570 m

See Section 5.7 below for shipping requirements.

Revised August, 2004

10 TEGAM WAY • GENEVA, OHIO 44041 • 440-466-6100 • FAX [phone]

• [e-mail]

2-1

PREPARATION FOR USE AND INSTALLATION

SECTION 2

PREPARATION FOR USE AND INSTALLATION

2.1 Unpacking and Inspection

Upon receipt, the R1M-A and accessories should be carefully
unpacked and removed from the shipping container.
Separate the units from the packing material and inspect
both the instrument and the accessories for any external
damage.

 If any dents, broken, or loose parts are seen, do not use

the equipment. Notify the shipping company immediately
and follow their instructions as to how to proceed.

 Check that all items are present. If any items are missing,

notify the shipper if this is a new instrument. If not new,
contact the previous user to locate the missing item(s).

2.2 Preparation for Use

Release the two latches which secure the lid and open the
lid. Remove the power cord and the two test cables which
are stored in the side compartment. If desired, the lid may
then be removed by pushing it to the right.
Set the ‘TEST VOLTAGE’ rotary switch to the desired value,
from 50 V to 500 V and set the ‘OHMS RANGE’ switch to the
anticipated range.
Note that although the ‘OHMS RANGE’ switch is marked from
1 M to 100 G, a 100% over-range capability is built into this
instrument.
Note also, that for resistance values less than 1 MΩ, the only
test voltage that should be used is 50 V. No damage will
occur if a higher voltage is selected, but the readings may
not be accurate. Do not measure resistors less than 50 kΩ
with the R1M-A; it may damage the instrument.

WARNING

SHORTING THE ‘TEST’ and ‘SIGNAL’ LEADS TOGETHER WILL

CAUSE INSTRUMENT DAMAGE.

Revised August, 2004

10 TEGAM WAY • GENEVA, OHIO 44041 • 440-466-6100 • FAX [phone]

• [e-mail]

2-2

PREPARATION FOR USE AND INSTALLATION

Power Up

Plug the power cord into a source of AC power (103.5 V to
129 V at 50 Hz or 60 Hz). Check that the other end is
plugged securely into the power input receptacle on the front
panel and turn on the POWER toggle switch.

Connections to DUT

One test cable has a double banana plug at one end and red
and black insulated alligator clips at the other end. This is
the shielded test cable. Connect the red alligator clip to one
end of the resistor under test. Connect the black clip to the
guard circuit, if any. If no guard is available, this clip may be
left floating (it is connected to the cable shield and to the
R1M-A guard circuit at the other end) however, this clip must
not be allowed to make accidental contact with any part of
the external circuit. Plug the dual-banana plug on this cable
into the SIG and GUARD binding posts. Note that the pin
marked GROUND should go into the GUARD binding post. If
there is no guard available and the black alligator clip at the
other end of the test cable is left floating, the operator may
choose to orient the dual banana plug so that the GROUND
pin is NOT plugged into the GUARD binding post. This will
ensure that any accidental contact of the black alligator clip
will cause no problem; however, the cable shield will then be
floating and the signal may be excessively noisy.
The other test cable has a shrouded banana plug on one end
and an insulated alligator clip on the other end. This cable
carries the high voltage output of the R1M-A to the resistor
under test. Connect the alligator clip to the other end of the
resistor under test; then plug the shrouded banana plug into
the recessed (RED) ‘TEST’ jack. Please refer to the
connection diagram (figure 1) below.

The shorting link on the GROUND binding post may be
swung around and connected to the GUARD binding post to
ground the R1M-A circuitry. This may be done only if there is
no external voltage with respect to ground on the measured
resistor or guard.

Revised August, 2004

10 TEGAM WAY • GENEVA, OHIO 44041 • 440-466-6100 • FAX [phone]

• [e-mail]

2-3

PREPARATION FOR USE AND INSTALLATION

Figure 1: Connection Diagram

Revised August, 2004

10 TEGAM WAY • GENEVA, OHIO 44041 • 440-466-6100 • FAX [phone]

• [e-mail]

3-1

OPERATING INSTRUCTIONS

SECTION 3

OPERATING INSTRUCTIONS

The R1M-A is designed for bench-top or field operation. Use
the cables connecting their banana plug terminations to the
appropriate connectors explained in Section 2.2.

WARNING

DO NOT TOUCH ANY ALIGATOR CLIP WHILE DEPRESSING THE
TEST PUSHBUTTON. LETHAL VOLTAGES MAY BE PRESENT ON
THESE CLIPS.

3.1 Rotary Switch Functions

The two rotary switches manually scroll through the six
resistance and four voltage ranges.
Full scale on any range may be described as 2,000 (actually
1,999), since this is a 3 ½ digit meter. If the readings are
exceeding 1,999 counts, step to the next higher range. If the
readings are less than 2,000 counts, step down a range, so
that it will read 1,999 counts, or less. The decimal point is
located automatically for the correct reading.
If the selected range is too low for the value of the resistor
under test, the display will show over-range by showing “1”
on the display. Similarly, the under-range condition is
displayed by showing negative readings on the display. “-1”
is displayed on the display until the test button is pressed.
The POWER switch turns on the power to operate the unit or
turns off the power to the unit. Note that when power is
turned off, it may take several seconds to discharge circuit
capacity to completely blank the display. The black markings
seen have no effect and disappear when power is turned
back on.

WARNING

TAKING RESISTANCE MEASUREMENTS ON A POWERED OR
ENERGIZED COMPONENT COULD CAUSE SERIOUS HARM
TO THE OPERATOR AND/OR DAMAGE THE R1M-A. BE
SURE THE ITEM TO BE MEASURED IS DISCONNECTED
FROM OTHER COMPONENTS AND APPARATUS.

Revised August, 2004

10 TEGAM WAY • GENEVA, OHIO 44041 • 440-466-6100 • FAX [phone]

• [e-mail]

3-2

OPERATING INSTRUCTIONS

3.2 General Theory Of Operation

A 2-terminal measurement method is used to determine the
resistance of the item under test. The R1M-A calculates the
resistance of the item under test utilizing Ohm's law and
displays it on a 3 ½ digit display.

To obtain the best accuracy, allow the R1M-A to warm up for
15 to 30 minutes before making measurements. In any case,
a minimum warm-up of 30 seconds is advised.

Depress the TEST pushbutton, which switches on the high
voltage. Note that the red LED will light, indicating that high
voltage is present on the terminal. Allow for a brief settling
time and read the resistance on the digital display. Note that
the operating range of resistance values which may be read
on any given range extends from 5% to 199.9% of the
nominal value of the selected range. Note that readings
greater than 100% will take more time. Thus, the 1 MΩ
range may be used to measure resistors from 50 kΩ to

1.999 MΩ. Note that the test voltage must be 50 V for
resistances less than 1 MΩ. If the resistance measured
exceeds the maximum value for the selected range, the
display will show blanks; in that case, set the range switch to
a higher range. If the resistance measured is less than 5% of
the nominal value of the selected range, the display will
show a minus sign; if so, switch to a lower range, since the
readings may be inaccurate.

If readings are noisy, especially at very high values of
resistance, it may be caused by 60 Hz coupled to the test
resistance from the power line. Note that at 100 GΩ, an
extremely small capacitance will couple many volts into the
test resistance from a power line. If so, it may be necessary
to interpose a grounded shield plate or to put the unknown
resistor into a metal box, connected to the GUARD alligator
clip.

To close up the R1M-A, first reattach the lid to the main
case, if it has been removed. Then store the power cord and

test cables in the side compartment.

Revised August, 2004

10 TEGAM WAY • GENEVA, OHIO 44041 • 440-466-6100 • FAX [phone]

• [e-mail]

4-1

PRINCIPLES OF OPERATION

SECTION 4

PRINCIPLES OF OPERATION

The power supply uses a transformer with two secondary
windings. The low-voltage winding is a center-tapped
winding. Diodes D9 and D12 provide rectified + power
filtered by C26 and regulated at +6 V by D7. Diodes D10 and
D11 provide rectified - power, filtered by C25 and regulated
at -6 V by D8. The high-voltage winding on T-1 charges C23
through D7 and C24 through D8. Since these two capacitors
are connected in series, this circuit functions as a voltage
doubler to provide a high voltage nearly equal to twice the
peak voltage of the high voltage winding. This high voltage is
at least 650 V at low line in order to provide 500 V test
voltage with 1 IDA of I x R drop across R37.

R37, a series resistor, is followed by Q1, a high-voltage
shunt regulator, to regulate the high voltage supply at the
selected value. R38 provides protection for Q1 from excess
current caused by external voltages. R6-R9 operate as a
four-section voltage divider, dividing the voltage from U2, a

2.5 V precision voltage reference, to 0.25, 0.5; 1.25, and 2.5
V. The voltage selected by S1 A, the ‘TEST VOLTAGE’
selection switch, is fed into pin 9 of U1, a quad operational
amplifier. The high voltage output is divided by R3 and R4 to
1/200 of the high voltage output. This divided voltage is fed
to pin 10 of U1, where it is compared with the selected
reference voltage. If the divided output is higher than the
reference, the output (pin 8) of U1 goes more positive,
increasing the base current drive to Q1. Since this is a shunt
regulator, the output high voltage decreases, until an
equilibrium point is reached. Thus, the high voltage is
regulated at the selected value.

When a resistor is not being tested, S3 (the ‘TEST’ switch) is
closed, shorting out the high voltage. This also provides
added safety in the event that the external circuit under test
contains capacitors. If so, they will be charged during ‘TEST’,
but discharged automatically as soon as S3 is released.