What it is and where you'll see it
The TM221PACKME16T: This Modicon M221 logic controller is the brain for a small machine — 16 I/O, eight transistor source outputs, two analog inputs at 0-10 V, and Ethernet baked in. It runs on 24 V DC and draws 35 A inrush at power-up, so size your PSU with a little headroom. Out on the line, I've seen these M221s hold up fine in light industrial cabinets — not much different from the old Twidos, just newer. The transistor outputs are solid-state, so no relay contacts to pit up on a cycling conveyor or pick-and-place cell.
How it stacks up against the TM221ME16TG
The natural sibling to this controller is the TM221ME16TG. Same Modicon M221 family, same 16 I/O count, same transistor output type, same Ethernet port. But look at the width: this one is 95 mm, the TG is 70 mm. That 25 mm difference means you can't slide this into a panel cutout made for the other without grabbing a file or moving a DIN rail. If you've already got a panel wired for 24 V and need room for a wider controller, this is the one. If space is tight and you have a serial supply handy, the TG fits. Both get the job done.
Mounting and wiring notes
Mounts on standard TH35-15 or TH35-7.5 DIN rail (IP20 with the protective cover on). The spring-cage terminal blocks take solid or ferruled stranded wire — strip to 8 mm. Dimensions: 95 mm wide, 90 mm tall, 70 mm deep. That's a compact footprint, but the width is the spec you need to check against your rail layout. The two analog inputs are 0-10 V, 10-bit resolution, with 100 kOhm impedance. Shield the cable at the panel end only to keep noise out. Discrete inputs are IEC 61131-2 Type 1, sink or source. You get nine inputs total — four of them fast inputs for HSC or pulse counting up to 100 kHz. Outputs are eight transistor PNP, 0.5 A each, with a maximum of 4 A per output common. The two fast outputs (Q0, Q1) handle PWM or PTO up to 100 kHz. For a small servo or stepper index, that's plenty.
Sourcing and compliance
Compliance documents (IEC 61131-2, UL 508, CSA C22.2, RoHS) are standard for this series, but I don't have the exact certs in front of me. Treat that as a reasonable expectation — not a guarantee — and check with your local distributor if your inspector wants hard copies.