ANENG ST213 Clamp Meter

For a total of $20.57, I received the ANENG ST213 Smart Digital Clamp Meter in 4 days (not bad for free delivery from China).  I have an ANENG AN8008 multimeter, which I have been generally pleased with.  I want to add a clamp meter to my measurement tools.

The meter looks slick and feels comfortable holding it.  It comes with one set probe and a K-type thermocouple.  The probe looks decent.  It takes two 2 AAA battery cells (not included).   If the battery voltage is less than 2.6V, the low-battery sign shows.  So NiMH batteries would have trouble staying above 1.3V per cell, but it probably still is functional at lower voltages.  Press the power button for two seconds to turn on.  The meter is in the auto mode, displaying temperature in Celsius and Fahrenheit (this is from the meter's internal temperature sensor since the thermocouple is not connected), which seems a little excessive to display the temperature so prominently when the thermocouple is not used.  There is an LED light at the top, which could be useful in the dark.

The "Smart" feature of the meter is that it tries to automatically determine what is being measured, AC/DC voltage, resistance with continuity beep, frequency and AC current.  But for resistance measurement, it is necessary to inject a signal, so the meter starts with voltage measurement and if the voltage is less than 0.5V, it switches to resistance measurement.  For low voltage measurement, it is necessary to manually select the mV measurement.  In many cases, it is probably not good to inject a signal and there is no way to manually select voltage measurement, which is the main deficiency of this meter.  And all measurements are autorange, no manual range selection.  This meter uses a single button for measurement selection and does away with the wheel, which can be a source of unreliability.

For voltage measurement, below 6V, the resolution is 1mV, which is good that the 5V circuit can be measured to 1mV unlike other meters that only go to 4V for the same resolution,  between 6V and 60V, the resolution is 10mV, and above 60V, 0.1V.  The voltage measurements generally agree with Fluke 87 DMM to 0.1-0.2%.  The accuracy holds up well above 100V.  

The resistance measurements agree with Fluke to 0.5%.  The meter beeps when the resistance is below 50Ω, which could be annoying.   Up to 0.5V could be applied.

For AC voltage, the RMS measurements seem good to 1KHz, with 3dB bandwidth around 3KHz.  The measurements agree with the Fluke to 0.6% below 1KHz.  The Fluke is still good at 10KHz with 3dB bandwidth over 100KHz.  Above 1V RMS, the frequency measurement works down to 6Hz; the resolution is 0.1Hz below 1KHz.

The main feature is the current measurement.  Below 0.3A, the current measurement is not useful; between 0.3 to 1A, the measurement error is around 10%.  Above 1A, the measurement error is about 2-3%, which is meeting the stated accuracy of +/-2.5% +/- 30 digits.  The initial offset can be nulled by pressing the REL|NCV button.  Note that it is possible to improve the low current measurements by looping the wire a few times around the clamp.  The jaw open to about 1".

For AC current measurement, the reading is 0 when the current is less than 0.6A and it is not expected to be accurate below 1A.  For a 100W light bulb, the Fluke reads 0.8A and this meter 0.63A.  When the Fluke reads 1.279A, this meter reads 1.15A, off by 10%.

It can also measure diode voltage and capacitance.  The max test voltage is 3.268V, and the max test current is about 2mA.  The test current is not constant, decreasing as the voltage increases.  The max diode voltages is about 3V, at which the applied current is about 0.16mA.  The capacitance measurements have a wider range than the Fluke, agreeing to about 5%.  

The NCV detection beeps when coming near a live AC wire (>90V).   It is sensitive enough to detect the live side of a wall socket.  On AC wiring, the live wire needs to be separated from the neural to be detected.  The Live wire detection uses only one probe; the actual detection threshold seems 1Vpp (tested with both probes connected).  These functions come handy in the household electrical work.

Dipping the thermocouple into molten solder, the temperature reading is 180C, which is about the melting point of 63/37 Sn/Pb solder.  At the other extreme, placing the thermocouple on dry ice, it drops to -40C and then shows OVLD (as specified).

This meter may be useful around the household and for automotive work, but not that good for lab electronics, especially because it cannot be locked in the voltage mode and making low current measurements.

Damaged Current Shunt Resistor in Cen-Tech Multimeter

The 20mA range current measurement stopped working on my Cen-Tech multimeter.  The other current measurement ranges still worked.  I suspected a damaged current sensor resistor, which is about 10Ω.  I opened up the meter and quickly identified a 9Ω resistor which was measured open.  And the discoloration indicated damage, which was probably a result of overcurrent.  A nearby 1Ω resistor also showed some discoloration, but was still intact.  The resistor is of size 0805, which probably has a power rating of 1/4W or less.  So the maximum current is 167mA at this rated power.  The fuse is rated 500mA, which would not be able to protect the resistor.  Once the resistor was replaced; it worked again and was checked against a Fluke 87 multimeter, the measurements are within 20uA of each other around 20mA, or 0.1%.  When it is compared with a Fluke 87, the Fluke uses a 0.991Ω 0.1% 2.5W resistor for mA range current measurement.  The maximum current is 1.6A, which is greater than the 1A fuse rating.

EBL Gold Pro AA NiMH 2800mAh rechargeable

EBL Gold Pro AA NiMH 2800mAh rechargeable low self discharge battery (90% after 3 years) , weighs 28.90g, costs about $1.87 per cell, or 1500mAh per dollar, which relatively inexpensive compared with other brands (Amazon Basic 1290mAh per dollar, Energizer 890 mAh per dollar, Eneloop 460mAh per dollar, POWEROWL 1320mAh per dollar).

Multiple users have showed that the actual capacity of EBL 2800mAh battery is only about 2400mAh.  The discharge rates for their tests are probably high to keep the testing time short.  Here we measure the capacity by discharging it at a low rate with an 80-Ohm resistor load.  We record the voltages over time and calculate the current and integrate to get the capacity.  At the average discharge rate of about 15mA, we expect it to take 7-8 days.  First it is charged from 1.28V for about 2hrs at 0.3A to 1.440V, which drops to 1.365V after about 1 day and 1.350 after 2days without load.  Then the measurements are taken with load.  It is fully discharged in about 150hrs and the capacity is 2338mAh.  More appropriately, the capacity is 2865mWh.  (Or 2388mAh if divided by the nominal 1.2V.)  In any case, it is only about 85% of stated capacity, consistent with other user reports.  Using the measured capacity, the cost is 1250mAh per dollar, on par with the Amazon Basic.  The big brand name batteries are rather overpriced (perhaps they are better in the number of charge cycles or internal resistance).

In a real-world test, it is compared to an Energizer 800mAh AAA NiMH battery (NH12 HR03) in a wireless mouse.  The Energizer AAA battery lasted about 1 month and the EBL AA battery lasted two months; tests were run twice and the results were similar.  This would imply that the EBL AA is only around 1600mAh, which is a huge disappointment. However, a Panasonic AAA eneloop 750mAh only lasted about half a month, which is a little surprising; if this is accurate, the EBL AA would have 2800mAh as advertised.  Panasonic AA eneloop 1900mAh lasted 2 and a half months.  More testing underway.