Multimeter Ceramic Fuse Replacement

If you need replacing a fuse on your multimeter, you may find this reading useful. In this post I will share with you where you can buy cheap replacement ceramic fuses and how to make your DMM accept 5x20mm and 6x32mm fuses. I will also give some information regarding fuses and counterfeit fuses. In this case I am replacing the 1A fuse on a Uni-T UT61E multimeter, but this is applicable to most multimeters. You can read my review and teardown of the Uni-T UT61E multimeter here.

Ceramic vs. Glass fuses

The Uni-T UT61E, like many "better quality" DMM's, uses ceramic fuses. Ceramic fuses are better than the more common and cheaper glass fuses. They have a feature called High Rupture Capacity (HRC). Ceramic fuses have a ceramic tube, and all the empty space inside is filled with sand. If a very high current occurs, an extremely high amount of heat is created inside the fuse. That heat melts the sand filling of the fuse into glass. Since glass is an insulator, it suppresses any arc-over instantaneously. This behaviour minimizes the possibility of a dangerous high arc current, which is what happens if a normal glass fuse fails to break a heavy fault current. Unlike sand filled ceramic fuses, if a very high arc current goes through a common glass fuse, it can generate an explosion that shatters the fuse and lead to damages and serious injuries. 

Sources of 6x25mm ceramic fuses

The Uni-T UT61E uses two ceramic fuses, one 6x25mm 10A and one 6x25mm 1A. The original fuses are branded AsiaFuse BS1362. Unfortunately, it turns out that cheap BS1362 6x25mm ceramic fuses are hard to find. The more common BS1362 6x32mm fuse size is available from multiples sources though. And since the Uni-T UT61E PCB layout accepts 6x32mm fuses also, it's just a matter of moving one of the fuse holder terminals to a different position. Take a look a the following picture.

In the above picture, since a 6x25mm fuse was not available, I managed to use a 5x20mm glass fuse temporarily while my order of 6x25mm ceramic fuses did not arrive. It was a matter of carefully tightening the fuse support until it hold the smaller 5x20mm fuse securely in-place.

These are the BS1362 ceramic fuses I received from AliExpress. They are branded Bussmann and costed US $2.50 for a pack of 10. And here is the Uni-T 61E after the 1A fuse was replaced.

Unfortunately, after careful inspection and despite apparent good build quality, the fuses I received appear not to be genuine. However, since I determined they are safe to use (read below), I'm happy.

Buy BS1362 ceramic fuses from Banggood!

Counterfeit fuses 

Since branded ceramic fuses are much more expensive than glass fuses, there are counterfeits with varying levels of quality. In many cases it's very hard to tell if a ceramic fuse is genuine or not. One can visually inspect and compare the suspect fuse with an original fuse sourced from a reputable distributor. If you buy a set of ceramic fuses I recommend you open one to see if it is really filled with sand. Needless to say, counterfeit fuses can be dangerous!

BS1362 Fuse Specs Datasheet
Counterfeit Fuse Information
Review of Uni-T UT61E

BSide ADM04 Mini Multimeter Review & Teardown

The BSide ADM04 mini multimeter is a 3 1/2 digit small and inexpensive portable digital multimeter with some special features. One of the features is the non-contact voltage detection (NCV) function. This enables you to locate hidden live mains wires behind a wall. The ADM04 mini also has a Hold function and LCD backlite, something that even some more expensive multimeters don't have. But that's not all, it also has a spotlight! Yes, press a button and you can turn your multimeter into a flashlight. So, this is clearly a multimeter ideally suited to be carried around. Lets take a closer lock at the BSide ADM04 mini multimeter.

Features:
3 1/2 digital LCD display.
Mini pocket Auto range digital multimeter.
Measure DC/AC voltage, DC/AC current, resistance, and diode & continuity check.
Data Hold function.
With NCV (Non-contact AC voltage detector) function.
With backlight and work light.
With protection case.
Low battery indication.
Auto power off.
Safety rating: CE CATIII 600V.

Specifications:
DCV: 200mV/2V/20V/200V+-(0.5%+3), 600V+-(0.8%+5)
ACV: 2V/20V/200V+-(0.8%+3), 600V+-(1.0%+5)
DCA: 200µA/2000µA/20mA/200mA+-(1.8%+5)
ACA: 200µA/2000µA/20mA/200mA+-(2.0%+5)
Resistance: 200Ω/2kΩ/20kΩ/200kΩ/2MΩ+-(1%+3), 20MΩ+-(1.2%+15)

General characteristics:
Operating Temperature & Humidity: 0~40°C(32~104 °F), <80% RH
Storage Temperature & Humidity: -10~60°C(14~140 °F), <70% RH
Product Size: 130x62x27mm(5.4"x2.5"x1.10")
Product net weight: 150g/0.34lb
Colour: Black + Blue
Power Supply: 2 x 1.5V AAA Batteries (NOT included)

Appearance

The first thing that catches your attention is the small size of the BSide ADM04 multimeter. Although not the World's smallest multimeter, it will fit a large pocket. The multimeter case is protected by a silicone sleeve. The silicone sleeve protects the multimeter from falls and prevents the multimeter from skidding on the work bench. You will also notice that the test leads are not the usual detachable banana type cables, but are instead attached permanently to the multimeter. Since the ADM04 does not have some functions that would require the use of more than two multimeter inputs, for example high currents measuring, there is no need for detachable multimeter test leads. The test leads appear to be of good quality. The probes have detachable sleeves.

Non-contact voltage detection function

To use the non-contact voltage detection feature put the multimeter rotary switch in any position other than Off and point the bumpy part of the top of the multimeter to where the wires would be. If live AC wires are detected an LED near the top of the LCD will turn red. My tests show that the multimeter can detect live AC mains wires behind walls as long the wires are not to far away or the wall is not made of cement. Mains wires should be easily detected in plaster walls. Detection distance will vary, but it should work at a distance of up to about 10cm.

Voltage test
Both DC and AC measurements where within the accuracy specifications.

Current test
Current tests where within the accuracy specifications. Note that the ADM04 multimeter is capable of measuring only up to 200mA maximum current.

Diode test

Diode test range is 1V with 0.001V resolution and about 1mA test current. The display shows the approximate value of diode forward voltage drop. Open circuit voltage is about 1.6V which will be a problem when testing some LED's.

Continuity test

The built-in buzzer sounds when the measured resistance is less than about 50Ω. Response time is not fast, but it's OK.

Hold function

Reading values can be frozen on the LCD by pressing the hold button. The multimeter does not have auto-hold function.

Backlight and flashlight

LCD backlight is turned On by pressing the backlight button for 2 seconds. Backlight turns Off automatically after 15 seconds. The flashlight consists in a white LED with a lens and is activated simultaneously with the LCD backlight.

Test leads

The test leads are rated 600V CATIII/1KV CATII. They appear to be of reasonably good quality and made from silicone wire. The probes have detachable sleeves.

Battery replacement

The BSide ADM04 mini multimeter is powered by 2x AAA batteries. The battery compartment can be opened by removing a screw on the back.

Fuse replacement

The multimeter uses a single 250V 250mA ceramic fuse. To replace the fuse it is necessary to open the multimeter case.

Tear-down

The multimeter can be opened by removing the protective rubber case and unscrewing four screws. The battery compartment connects to the main board by two springs.

The multimeter uses a single board design. Component layout is good without any bodge wires in sight. Soldering is also good.

Input protection is accomplished by a single 250V 250mA ceramic fuse, two PTC's, diodes and resistors. Since this multimeter does not have a high current input, the usual wire current shunt and high current fuse are not present.

Verdict

The BSide ADM04 mini multimeter is a 3 1/2 digit portable digital multimeter with some welcomed added features and good build quality. The multimeter comes with a user manual in good English, something that more often than not is not the case. If you don't need to measure currents higher than 200mA, this is a good little multimeter to carry around. It is adequate for low voltage, low current circuits.

BUY THE BSIDE ADM04 MINI MULTIMETER FROM BANGGOOD

Need a better multimeter? Then take a look at my Uni-T UT61E multimeter review.

New to multimeters? Read my Multimeter buying guide.

Uni-T UT61E Multimeter Review & Teardown

In this post I will be reviewing the Uni-T UT61E digital multimeter. The UT61E DMM is one of the most popular multimeters available. But is it any good? Lets find out!

If you are looking to buy a multimeter then please read my previous post where I give some advice on choosing and buying a multimeter.

The Uni-T UT61E is part of the UT61 family of DMM's from Uni-Trend Technology, a well known Chinese test and measurement solutions provider. You can choose from several models: UT61A, UT61B, UT61C, UT61D and UT61E. The models all look the same but they have different features and specifications. So compare the different models carefully before buying or you might get a bad surprise!

Uni-T UT61 Features

These are the common UT61 multimeter series features taken from the Uni-T web site:

1、Large LCD screen；

2、High resolution analog pointer display；

3、Full range overload protection；

4、Data hold, REL, Peak value measurement；

5、Low battery indication；

6、External interface supports RS-232C and USB cable.

UT61 Series can measure AC/DC voltage and current (UT61D, UT61E has true RMS), resistance, diode, circuit continuity, capacitance, frequency, temperature, hFE, electromagnetic induction, etc. UT61 Series complies with the standard IEC61010: CAT. III 1000V, CAT.IV 600V. 

And these are the specifications and feature list for the UT61E model:

Specifications	Range	Best Accuracy
DC Voltage (V)	220mV/2.2V/22V/220V/1000V	±(0.1%+2)
AC Voltage (V)	220mV/2.2V/22V/220V/750V	±(0.8%+10)
DC Current (A)	200μA/2200μA/22mA/220mA/2.2A/10A	± (0.5%+10)
AC Current (A)	200μA/2200μA/22mA/220mA/2.2A/10A	±(0.8%+10)
Resistance (Ω)	220Ω/2.2kΩ/22kΩ/220kΩ/2.2MΩ/22MΩ/220MΩ	±(0.5%+10)
Capacitance (F)	22nF/220nF/2.2μF/22μF/220μF/2.2mF/22mF/220mF	±(3.0%+5)
Frequency (Hz)	10Hz-220MHz	±(0.01%+5)
Features
Display Count		22000
Auto Range		√
True RMS		√
Bandwidth (Hz）		45Hz ～10kHz
Duty Cycle	0.1% ～ 99.9%	√
Diode		√
Continuity Buzzer		√
Low Battery Indication	≤7.5V	√
Data Hold		√
Relative Mode		√
Peak Value		√
RS-232		√
Analogue Bar Graph		46
Input Protection		√
Input Impedance for DCV	Around 10MΩ	√
General Characteristic
Power	9V Battery（6F22)
LCD Size	65mm × 43 mm
Product Color	Red and Grey
Product Net Weight	370g
Product Size	180mm × 87mm × 47 mm
Standard Accessories	Battery, Test Lead,Muli-Purpose Socket,RS-232 Interface Cable,PC Software CD
Standard Individual Packing	Gift Box, English Manual
Standard Quantity Per Carton	22 PCs
Standard Carton Measurement	455mm×335mm×375mm
Standard Carton Gross Weight	15.5 Kg
Optional Accessories*	USB Interface Cable

If you compare between the models, you can see that the UT61E has the best specs. It is a 22000 count DMM with better accuracy. However, it does not have LCD backlight (although it's possible to add it) and doesn't take temperature measurements.

UT61E Teardown pictures
The UT61E comes apart easily by turning just 3 screws.

Once opened you have access to replaceable components, like the 2 fuses. These are ceramic good quality fuses, not cheap glass fuses. As it can bee seen, the resistor network is now shielded. An improvement over previous UT61E versions.

Removing the PCB exposes the top PCB layer with the rotary switch. The main multimeter chip is the Cyrustek ES51922 (ES51922A). True RMS feature is implemented by use of the AD737J True RMS-To-DC converter chip.

To replace the battery only one screw needs to be unscrewed. 

Safety - Input protection

When I disassembled my Uni-T UT61E I got a very nice surprise! I immediately noticed that my UT61E has better input protection than expected. As you can see, the PCB has been redesigned and (among other improvements), there are additional input protection components on the PCB compared to other UT61E's. So, it seems Uni-T has improved the input protection on the Uni-T UT61E. There is however still room for input protection improvement. Markings for additional input protection components can bee seen on the PCB board. The following image shows the two different versions of the UT61E:

Two different versions of the UT61E

The PCB of my UT61E (on the right) is marked 150507-9C, while the other one is marked 150507-7.

Although there are no safety certification markings on the multimeter itself, on the box there is some reference to UL certification.

Accessories

The multimeter comes with a pair of test leads, multi-purpose socket, RS232C interface cable (USB available at extra cost) and software on CD-ROM. The multi-purpose socket inserts on two of the multimeter inputs and enables component testing without the probes. It accepts components with wire leads and smd components.

Accuracy testing

I have tested the UT61E accuracy with an AD584 high precision voltage reference module. The module has four reference DC voltages: 2.5V, 5V, 7.5V and 10V. All readings where well within the UT61E accuracy specifications. Since I do not have high enough precision resistors and capacitors I did not test the accuracy of these measurements. However, readings seem correct and, since the precision of low DC voltages are usually the most important, I don't worry about it. Please watch the YouTube video bellow:

Data logging
One of the major features of all Uni-T UT61 multimeters is its data logging capability. With data logging you are able to automatically record measurements from your multimeter to a computer. The provided software is somewhat basic, but it is simple to use. Connection is made by the provided custom RS232C cable. Connection with the multimeter is optical, so it is isolated and safe. If your computer doesn't have an RS232 serial port (many don't) you can use an serial to USB adapter. The interface software, driver and PDF manual come in the CD-ROM, but can also be downloaded from the official Uni-T UT61E page. Current version is 4.0.1.

Other tests and thoughts

The UT61E also passed the continuity test. It has a reasonably quick response when you short the test leads, but be sure the tips are making a good contact. Measurements are reasonably quick too. Only high value capacitors take more time to get a stable reading, but this is expected and is mentioned in the manual. According to the ES51922 specs, it can make two measurements every second and I think that's about right.

The selector switch is not top quality. It's not too loose or to hard to turn, but it's not very precise. I don't think this is a problem tough. 

Data logging works without problems, but I would prefer the multimeter came with a USB cable instead of RS232. Most computers don't even have the RS232 serial interface anymore! But again this is not a big issue because you can use an RS232 to USB adapter. 

If you are one of those people that never reads the product manual this is not an issue for you. But you should read the manual and, although it is fairly extensive, it's unnecessarily confusing. It is confusing because Uni-T supplies the same manual for all versions of the UT61 multimeter. So, some things apply to one model but not others and you have to pay attention.

  
Verdict

I find the Uni-T UT61E is an excellent budget digital multimeter. I have the UT61E for some time now and it has not disappointed me yet. With its 22000 counts large and clear display, True RMS, PC connectivity and improved input protection, the UT61E has to be one of the best multimeters you can buy for under 50 USD.

Want to buy a Unit-T 61E?

I buy most of my electronics, tools and measuring equipment from Dealextreme and Banggood in China. They have low prices, friendly and helpful staff and will offer a solution if something goes wrong with your order. They have warehouses in Europe and the USA and can provide faster delivery for many of the items. I may get a small fee if you buy from them through links in MakerCorner. Thank you for your support!

Buy the Unit-T 61E from Dealextreme

Buy the Unit-T 61E from Banggood

Download the Unit UT61E user manual here.
Download Uni-T UT61E interface software and manual here. 

Multimeter buying guide

The multimeter is one of the most useful tools to anyone working with electronic or electrical devices or circuits. The basic multimeter is capable of measuring voltages, currents and resistances. A continuity test buzzer is also found on all current models. Many models, even cheap ones, are also capable of measuring temperatures, capacitances and frequencies. You can use a multimeter for something as simple as detecting a broken wire, measuring battery voltage or something more challenging such as finding a faulty transistor on a complex circuit. In this post I will share some essential information about multimeters and some advice for multimeter buyers. 

How multimeters work?

The working principle of a multimeters is really simple. Multimeters work by comparing external readings taken with two probe wires against an internal reference voltage. The result of the comparison is then shown on an LCD display in case of a digital multimeter or a panel meter in case of an analog multimeter. The accuracy of the multimeter measurements is directly related to the accuracy of the reference voltage. Most portable multimeters are powered from one 6F22/6LR61 9V battery or two AA 1.5V batteries.

Portable multimeters and bench multimeters
Multimeters can be of the portable or bench (fixed) type. A typical bench multimeter will have one or more bigger displays, bigger knobs and switches and more inputs. They are mains (AC) powered. In this post I will address portable multimeters.

Digital vs. Analog multimeter

Until the late 80's early 90's most multimeters where analog. The analog multimeter is easily identified by the meter panel with its big needle. Analog multimeters are fine, but they are less precise than digital ones and take more time to display the measurements. Nowadays digital multimeters are so cheap that anyone can afford one or more! 

Multimeter features

A basic multimeter will measure AC and DC voltages, DC currents and resistances. Most will also have a continuity test (buzzer) and a diode test mode. Many models will also feature temperature, capacitance and frequency readings. Some will have true RMS readings. Another useful feature is automatic data hold. One feature that is commonplace in cheap multimeters but not in more expensive ones is the transistor tester function. This is the case because it's a rarely used feature and cheap multimeter manufacturers try to offer as many features as possible to captivate potential buyers.

Multimeters are capable of taking measurements across a wide range of values. For measuring and display purposes this wide measuring range must be split into several narrower ranges. A multimeter with more ranges is more desirable than one with fewer ranges, because it will allow for better accuracy. Many digital multimeters have the autorange feature, which means that range selection is done automatically by the multimeter. Display resolution is limited by the number of digits of the display and the multimeter chip. A 3 1/2 digit display multimeter will display values between -199 and 199. A multimeter with a 4 1/2 or more digits display will allow for more resolution. If speed of measurements is important, higher quality multimeters usually are faster at taking readings.

Multimeter safety

Since most multimeters are capable of measuring high voltages and currents, they must protect the user from any accidental over-voltage discharge or over-current. The most basic protection is given by one ore more fuses on the multimeter inputs. Good quality multimeters will have other additional protection components like VDR's. For protection purposes multimeters are classed according to the level of protection built-in as CAT II, CAT III or CAT IV and a certain maximum voltage level. But, even if a multimeter is claimed as having CAT III or CAT II level protection, this might not be a guaranty of safety, specially with very cheap multimeters from unknown brands. I don't recommend connecting a cheap multimeter to the mains power without first opening the multimeter and checking visually the quality of the protection circuit, soldering and wiring. If you are going to use the multimeter for low voltage low current applications then, safety wise, any cheap multimeter will do the job.

Inside a 20 USD digital multimeter

Are cheap multimeters any good?

Yes and no. For starters it depends on your definition of 'cheap' and 'good' and what you expect from a multimeter. You can buy a very acceptable basic multimeter for low voltage applications for just under 10 USD! Build quality aside, generally a multimeter will be more expensive if it has higher precision and accuracy. It will also be more expensive if it offers better protection (safety!). You are not going to find a general purpose good quality multimeter for 10 USD, 20 USD or probably even 30 USD. However, if you are not going to measure high voltages or currents (like mains power), the level of protection found on a cheap multimeter is usually good enough. So, if you are not going to measure mains voltages but just low voltages, fear not buying a cheap multimeter.

Three cheap multimeters: 5 USD (left) and 20 USD (center and right).

A better multimeter: the Uni-T 61E.

How many multimeters should I have?

It is advisable to have at least two multimeters. There are several reasons but, for starters with two multimeters you can make measurements with two different devices, greatly reducing the possibility of inaccurate readings. If you only have one multimeter, a faulty multimeter might go unnoticed and trick you. If you have two or more multimeters you can immediately check one against the other and realize that one of them is faulty. It's also often necessary to check voltages in more than one point in a circuit at the same time. Or, you might need to measure voltage and current at the same time.

Final advice

There are many models of digital multimeters, with different features, various degrees of quality and prices. Usually you get what you pay for. Don't expect miracles, quality costs money. Check what's available. Make a list of the features you need or value more and those that are desirable. Choose a multimeter rated for the highest category you could be working in. Then, look for a voltage rating for that category matching your needs. Use Google to get the multimeter's full specs and, if possible, the user manual. Google for user reviews. Good luck!

Need to buy a multimeter?

I buy most of my electronics, tools and measuring equipment from Dealextreme and Banggood in China. They have low prices, friendly and helpful staff and will offer a solution if something goes wrong with your order. They have warehouses in Europe and the USA and can provide faster delivery for many of the items. I get a small fee if you buy from them through links in MakerCorner. So, please support my work by clicking on the following links. Thank you!

Buy a multimeter from Dealextreme
Buy a multimeter from Banggood