The optical gate of meter reading: the standard, the handshake, DLMS and field practice — all in one place.
The small round window on electricity, gas and water meters is the infrared communication gate defined by IEC 62056-21 (formerly IEC 1107). While the meter stays galvanically isolated from the grid, it opens a safe serial channel to the outside over 880 nm infrared light.
The optical probe (optical reading head) docks onto this window with a magnetic ring and translates the meter's language of light into serial data computers understand. All six meteroptic models share the same optical head; only the interface on the other end differs.
Reading always starts with the same ritual: the probe sends a request at 300 baud 7E1, the meter answers with its identification line — manufacturer code, baud identifier and model. An acknowledgement follows and both sides switch to the agreed speed (typically 9600 or 19200) before data mode begins.
The timing of these transitions is delicate and entirely between the software and the meter; meteroptic probes never interfere, tracking the baud change losslessly at the physical layer.
Modern meters advertise mode-E capability in their identification line: the parties switch from the ASCII protocol to binary HDLC frames and a DLMS/COSEM session is established. Registers, demand and load profiles are read in this session, addressed by OBIS codes.
To the probe there is no difference: bits become light, light becomes bits. This transparency lets the same hardware serve both legacy IEC readout and current DLMS infrastructures.
In Türkiye, meter-reading infrastructure is shaped by TEDAŞ specifications: OSOS remote-reading systems and the MASS communication standard. The optical port is the indispensable tool for commissioning, diagnostics and on-site verification in this ecosystem.
meteroptic probes are designed to work with the modems, handheld terminals and head-end software of this ecosystem, meeting the optical-port requirements of the specifications.
On the wired side there are three paths: MO-USB for desktop software and test benches, MO-485 for permanent panel installation, MO-TTL for embedding into your own board.
On the wireless side: MO-BLE for mobile apps, MO-SPP for existing software expecting a virtual COM port, MO-WIFI for continuous access over the network. Undecided? See the comparison table on the homepage or write to us.
The magnetic ring must sit centred on the window; a misaligned head is the most common cause of read errors. On meters in direct sunlight, shading the head by hand stabilises the reading.
Do not forget the termination resistor on long RS-485 lines. On battery models, do not send commands before the RDY LED is on; bytes sent before pairing completes are lost.