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User Manual of BM3548 and BM3549 

Insulation Tester and Multimeter 

Distinguished users: 
      Thank you for purchasing the meter of our company. To use the meter 
correctly, please read the operating instructions thoroughly and carefully before 
use it, especially the section of “Safety information”. 
Please keep the operating instructions in a safe place after reading it, putting it 
where the meter is or keeping it in handy for future reference. 
 

  Attention: A test cable is provided for the meter. It is not allowed to 

perform insulation test by holding the test cable with your hands. Ensure 
that the to-be-tested object is securely clamped and keep your body away 
from the circuit before press the TEST key to output high voltage.

 

I. Overview 

Welcome to use the product! 
BM3548/49 digital multimeter with auto range selection is a real digital 

insulating resistance digital millimeter. It has features of complete 
functions, high accuracy, reliability in operation, and convenience in use. Output 
test voltage can be switched among 250V/500V/1000V/2500V, depending on 
different models. An ordinary insulating resistance meter can not measure the 
output high voltage of its own. When the output high voltage of the insulating 
resistance meter doesn’t conform to the rated value, it is not easy for the user to 
find the unconformity so that deviation of the measured result is over large 
sometimes and causing hidden troubles in safety. BM3548/49 can monitor the 
output high voltage in a real-time way. At any time, the user can observe actual 
measurement voltage that is output by the meter, effectively avoiding 
misjudgment caused due to output voltage not conforming to the rated value. 
The measurement range of the meter can reach up to 40G

. The measurement 

time can be set up according to requirements. After a measurement is completed, 
the measured result can be kept automatically. Functions of the digital 
multimeter include AC/DC voltage, current, resistance, capacitance, frequency, 
diode, and ON/OFF measurement. The functions of the digital multimeter are 
completely separated from those of the insulating resistance tester. When use 
functions of the multimeter, you need not be worried that you would suffer 
electric shock due to high voltage generated by the insulating resistance tester. 
The product is applicable to measurement of the insulating resistance of various 
insulating materials and electric equipments such as transformers, motors, 
cables, switches, and electric apparatuses. It is also applicable to maintenance, 
test, and inspection of various electric equipments. It is compact in structure, 
convenient to carry, and an ideal electrical and electronic testing meter of yours. 

II. Safety information 

  (1) Description of safety marks: 

 

  Warning:    important safety information the user must read

 

 

  Danger: high-voltage electric shock is present

 

 

 Double-insulated protection 

(2) Read the operating instructions carefully before use the meter. 
(3) It is strictly prohibited to use the meter before its rear cover is put in place. 

Otherwise, it might cause an electric shock. 

(4) Check and make sure the insulating layer of the test cable is in good 

condition without any breakage. 

(5) To avoid electric shock, do not touch the test cable and the circuit under test 

when performing a test. 

 

1

(6) Make sure one end of the test cable is securely inserted into the terminal. 
(7) During test, any range must not exceed its specified maximum input value. 
(8) During test, do not operate the switch knob for changing a range to avoid 
damaging the meter. 
(9) DC voltage over 50V or AC voltage over 36V can cause danger of electric 
shock. Be careful when taking measurement. 
(10) Before performing insulation test, make sure the range selection switch has 

been set within an appropriate voltage range. 

(11) Do not perform insulating resistance test in a combustible environment. 

Spark may cause explosion. 

(12) Stop using the meter, if its case or test cable is broken during use and the 

metal is exposed   

(13) When open the rear cover for changing battery, make sure the test cable has 

been removed out of the test terminal and the range switch switched to 
OFF position. 

(14) Take the battery out when the meter will not be used for a long time. 
(15) When “

-  +

 

” is displayed in the meter, it is necessary to change the battery 

in time to ensure measurement accuracy. 

 
 
 

 
 
 

 
 
 
III. Name and function of parts (see the figure) 
 

 

1

 

Function switch knob   

    Switch among power ON/OFF, measurement voltage of the insulating 
resistance, and various functions of the multimeter. 

2

TEST/STOP key:

 it is used to measure the insulating resistance 

RANGE key: it is used to switch between hand-operated and auto range mode 
as the meter is used as the multimeter. The function is not available when the 
meter is used as the insulating resistance tester. On startup, the meter is preset 
to auto range mode. Press the key to switch to hand-operated range mode. In 
hand-operated range mode, every time press the key, the range goes up one 
level until to the maximum level. After the maximum level is reached, every 
time press the key, the range goes to the minimum level. The process is 
repeated. If press and hold the key over 2 seconds, the meter is switched to 
auto range mode. 

3

SELECT key:

 it is used to set the measurement time of the insulating 

resistance as well as various function switch of the same position 

4

DH/BL key   

    Data hold/backlight function: press the key to lock the displayed result. 
Press it again to restore normal measurement (when OL is displayed in the 
meter, Hold function is not available). Press and hold the key for 2 seconds to 
switch between backlight on/off (in adjustment mode, backlight is not 
available). 
5

L (LINE) 

input terminal (connected to line terminal of the to-be-tested 

object). 

  6

V/

/mA/Hz/CAP

 input terminal: common positive input terminal of the 

digital multimeter; 
  7

COM/G

 input terminal (COM is common EARTH of the multimeter /G is 

shielded terminal of the insulating resistance). 
  8

E (EARTH)

 input terminal (connected to EARTH terminal of the 

to-be-tested object) 
  9

Liquid crystal display 

Small 8888

: measured value of high voltage 

of the insulating resistance 

-8888

: measured value of various functions 

Min

: measurement time of the insulating 

resistance (minute) 

OL

: overflow display, indicating the measured 

value exceeds the maximum display value. 

ERR

: indicating that serious current leakage 

or short circuit occurs to the equipment   

-  +

: Battery capacity is insufficient 

  10 Indicator light of high voltage 
  11 Holding box of the test cables   

 

12 Ring used to fasten the hanging strip 

IV. General characteristics 

(1) Auto range: “OL” will be displayed for overload. 
(2) Display mode: Liquid crystal display; maximum display: 4000

 

(3) Sampling rate: 2 times per second

 

(4) The meter can display actual insulation test voltage. LED light is used to 
indicate high voltage output status

 

(5) Operating environment: 0

°

C-40

°

C, less than 75%RH

   

(6) Storage environment:-10

°

C-60

°

C, less then 80%RH

   

(7) Maximum power consumption: 4.5W; minimum power consumption 18mW. 
(8) Indication for insufficient battery capacity: “

- +

” is displayed

 

(9) Power supply: 6 pieces of AA 1.5V battery (LR6×6) 
(10) Auto power off: The multimeter is turned off automatically in approx. 15 

minutes after it is turned on if no key is pressed or the knob is not turned. 

(11) External dimension: 170(length)×156(width)×64(height)mm  

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