Norma DM950

Norma DM9x0

Status	in progress
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.

It seems that the same device series was sold with two different names and designs:

• Norma Normameter 910..950 (red company sign and bumper; older)
• LEM Norma DM910..950 (turquoise company sign and bumper, see pics; newer)

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 separately as an accessory.

Hardware

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:

• 

  Front (with rubber holster)

• 

  Front and sides (with holster)

• 

  Back (with holster)

• 

  Front (without holster)

• 

  Back (without holster)

• 

  Battery case opened

• 

  Board without RS232 interface board

• 

  Inside with RS232 interface board installed

• 

  Interface board, back side

• 

  Interface board, front side

RS232 cable:

• 

  Printer Cable (original) and PC Adaptor (look-alike)

• 

  Printer Cable, multimeter side opened, components side.

• 

  Wires, contact pins, power plug side

• 

  Different angle

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

• http://www.set.nl/LEM/dmm.htm