Motive

Althougu Enoki uses DSO Measurements as voltage measurements, DMMs can measure current only. But one of them is poor a little. Enoki bought a cheap 1A ammeter at Aliexpress and evaluated the error.

Summary

The meter has 2mA dead zone at zero. It is not capable for measuring small current. It is an indicator that has some error. If you read minus 3mA, it may have within 0.5% error.

It has a 50 mΩ detecting resistor. We cannot get the value resistor in Japan. The detecting resistor is very valuable, Enoki thinks.

経緯目的

電圧は DSO の Measurement 機能をデジボル代わりに使用しているが，電流計は DMM に頼っている。安価なパネル メータがその代替にならないか試す。

要約

2mA の不感帯があり，微小電流の測定には不適。指示値を 3mA 低く見積もれば，精度 0.5% になる可能性がある。 精度 0.1% の 100 mΩ が入手可能な最小抵抗だ。入手難の検出抵抗は価値がある。

The specification is as follows, Accuracy: 0.1%
Refresh rate: Approx. 200 ms
Display: 3 digits 0.36" digital tube

Range: 999mA
Power supply: 4 to 30V
Working current: less than 8mA
Reserve temperature: -10 to + 65°C

Input impedance : 50 mΩ
Display color: Red/Blue/Green/Yellow

Dimensions: (L * W * H) 3.42*1.85*0.85 cm/1.35 "* 0.73" * 0.33"
QTY: 1 pc

I supplied it with 4V, and confirmed to work.

I looked up the sensitivity near zero, referring to DMM PC510 ammeter as shown in Figure1. Power supply is 5V.

I changed load resistor (3.3k, 2.4k, 2.2k, 1k, 330) to change current.

The device has 4 wires. The thin ones are power lines. The thick white one is detecting Positive line. The both black ones are the same ground.

Next, The variable voltage power supply DM-31OMV supplied a fixed 2Ω10W changing current, as shown in Figure2.

Photo1 shows to find the ammeter sensitivity or resolution at zero. Photo2 shows the ammeter indicating current value to find the error.

Photo1 Sensitivity

Photo2 Error

Figure3 Dead zone near zero

Figure3 Error correction

The ammeter has 2mA dead zone sensitivity. So if you measure 200 mA, it concludes 1% error.

Figure3 shows that the ammeter has +3mA error at least. So if you read 3mA less, the error satisfies less than 0.5% reading error.

I wanted to use the meter for calculating efficiency DC-DC converter that works under less than 100 mA. But it is not good for the purpose.

Enoki has a plan to make a power supplies more than 0.25 A. The meter may be useful for indicating the current.