Norma DM950

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Norma DM9x0
Norma DM950 1.JPG
Status planned
Counts 21000
IEC 61010-1 CAT II 600 V, CAT III 300 V
Connectivity RS232, proprietary cable
Measurements voltage, current, resistance, capacitance, temperature, diode, continuity
Features autorange, data hold, bargraph, (backlight)

The LEM Norma DM9x0 Series of multimeters are 21000 count CAT II/CAT III hand multimeters with optional RS232 connectivity. The models differ by precision and feature set.

They were also sold as OEM devices by Siemens.

The manufacturer was a company named Norma, later LEM Norma in Austria.

Models

Model Siemens OEM Precision (DC) Backlight RMS TRMS R 20 MΩ R 200 MΩ U AC 1 kΩ/V I 10A f C
Norma DM910 B1024 ±(0.5% +2d)
Norma DM920 B1025 ±(0.5% +2d)
Norma DM930 B1026 ±(0.3% +3d/+2d)
Norma DM940 B1027 ±(0.1% +3d/+2d)
Norma DM950 B1028 ±(0.06% +3d/+2d)

The RS232 interface is optional. All models were available with or without RS232 interface, the RS232 interface was also available as an accessory.

Hardware

Multimeter

Interface

The RS232 interface consists of the following components:

  1. Interface board (installed inside of multimeter, based on a NEC 75P116 microcontroller)
  2. Printer cable 5-pin to DB9
  3. PC adaptor (Null modem plug with slightly unusal pinout)

The RS232 interface is designed to allow a direct connection to a serial printer or data recorder. Therefore an adaptor is required to connect it to a PC.

Comm parameters (PC): DTR on, RTS off, RTS/CTS flow control (!).

If the interface cannot be powered from RS232 (e. g. RS232-USB converter with too low voltage), switching on the multimeter with the FUNC button pressed powers the interface from multimeter.

The interface board contains a battery-buffered clock and NVRAM memory.

The printer cable has got a power connector (10-16 V DC, 50 mA) to power the multimeter and the interface externally. Opening the plug on multimeter side should be avoided, if possible, because the nut on the opposite to the screw is loose beneath the rubber bumper and it can be a bit tricky to get it closed again without removing the glued bumper.

Photos

Multimeter:

RS232 cable:

Protocol

Printer Mode

TODO

PC communication mode

The multimeter supports about 50 commands, most functions that do not require changing the position of the rotary switch can be remote controlled.

Command Reply Example Remarks
IDN? Device id and rev., interface rev. 1834 065 V1.06,IF V1.02\r
DATA?\n 27 chars ASCII + \r R␣␣␣␣␣␣␣␣␣␣␣␣␣149.10E+3␣OHM\r Similar to common 14 char protocol, but more verbose. ␣ means space.
STATUS?\n 20 hex chars + \r 03030024913100400040\r Binary data, value + status flags.
... .. .... More to do.

Resources