New toy- Yokogawa CL 220 clamp meter

The thing is tiny! Shown next to the EEVblog uRuller

The thing is tiny! Shown next to the EEVblog uRuler


I’ve been looking for a good clamp meter for a while now. While there is plenty of no-name cheap meters on Ebay, I figured I’d wait till something better “washes ashore”. So when a Yokogawa meter got caught in my ebay filters one day, I grabbed it. Yokogawa is a Japanese company, well known for their power measurement equipment. This meter has a nice mix of AC and DC current ranges fitting my low to medium current measurements needs. It is also a recent model, still being made and supported- a rarity in my lab setup of 20+ year old equipment

This is a 4000 counts auto-ranging instrument with reasonable resolution (10mA)  and accuracy:

Manufacturer's specs

Manufacturer’s specs

Using it:

The meter is tiny and is as simple to use as they come- set it to DC or AC current, clamp over the wire you are measuring current in and get a number. Ideally you also hit a “Zero” button with the meter in place and current off to cancel out various ambient effects. The Data Hold button grabs the current reading and holds it on screen. Subsequent press turns it off. Autosleep kicks in after 30 seconds of user inactivity (keypresses or switch). Two LR44 button cell batteries are used, with a claimed continuous operating life of 100 hours. There is also an interesting accessory sold separately:

Adapter 99025

Adapter 99025

“Take it apart “

Back side

Battery compartment. It requires pushing in the locking pin with a suitable object to unlock. A bit of a pain

Very clean and simple interface

Uses two LR44 button cells

Top cover off

That’s a lot of adjustments!

Potentially a bodge

The board is held in by these removable plastic clamps

The top of the board holds LCD display, main microcontroller under it (with enough goop to kepe me from prying it off), and the adjustments trimpots. The back side is a collection of JRC (formerly NJR) NJM2121 and   NJU7702  as well Analog Devices OP196 and OP296 opamps, performing signal conditioning

Back of the board. Mode switch on the right.

Current measurement:

In basic DC measurement tests the meter was pretty close to my reference (Agilent U1252A):

Load setting CL220,A AgilentU1252A
10mA 0 10mA
40mA 0.04 39.8mA
50mA 0.05 50.2mA
100mA 0.1 99.9mA
150mA 0.14 149.5mA
200mA 0.19 200mA
500mA 0.49 498.8mA
1A 0.99 997.7mA
2A 1.98 1.995A
3 2.98 2.987A

Power consumption:

  • Claimed: 9mA active
  • Measured: 6mA




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