Voltcraft VC-350e

Voltcraft VC-350e

Status	in progress
Counts	4000
IEC 61010-1	CAT II (750 V AC/1000 V DC)
Connectivity	RS-232 (DB9)
Measurements	voltage, current, resistance, diode, continuity, temperature, frequency
Features	autorange, hold, bargraph

The Voltcraft VC-350e is a 4000 counts, CAT II (750/1000V) handheld digital multimeter with RS232 connectivity.

It is an OEM version of the Saftec SAF350E. The device was sold by Conrad Elektronik as article 125512 around 1997 and is not available any more.

Hardware

Multimeter:

• Multimeter IC: Maxim MAX134 datasheet
• CPU: SAF350E
• Fuses: 800mA/250V 5x20mm and 20A/250V 6x30mm (superfast, ceramic fuses)
• Battery: 9V NEDA 1604 or 6F22

RS232 hardware:

• Transfer rate:1200 baud
• Characters: 8-bit
• Parity:none
• Stop bits:1

This device uses what looks like a Metex connector, but it only has 4 pins (where 5 pins is seen on other devices).

Cable pinout

Metex-connector pin (male)	RS-232 DE9-female pin	Signal (multimeter side)	Remarks
1	3	RxD
-	-	empty space	space between pin 1 and 2 on Metex where there is no pin/hole.
2	5	GND
3	2	TxD
4	6, 7	DSR + RTS	DSR and RTS tied together on PC side

Serial protocol

To test on a Linux computer using the screen command, open a terminal like xfce4-terminal, gnome-terminal or xterm and start a session, we will use this terminal to display the data coming from the multimeter:

/usr/bin/screen -d -m -S serial /dev/ttyUSB0 1200

screen -r serial

Then open a new terminal to send commands to the multimeter, example to read the current measurements:

screen -S serial -X stuff "$(echo -e '\xE0\xFF\r')"

Output something like "012.003 V". Often the units show garbled, aka you will see "012.003 �" or something especially when using Ohms. I remember I also had this with the original vendor software (which I no longer have). So maybe my device is poor or it was just never developed better.

Serial protocol

Taken from the manual found at [1] this is the part that also works on Voltcraft VC-350e:

Resources

• Manual
• Polish forum with the only resource for the protocol

Measurement functions and ranges

Measurement function	Range	Resolution	Accuracy	sigrok result	Remarks
V=	400.0 mV	100 μV	±(0.5% + 3)	mq V, unit V, mqflags DC	"
	4.000 V	1 mV		"
	40.00 V	10 mV		"
	400.0 V	100 mV		"
	1000 V	1 V		"
V≈	400.0 mV	100 μV	±(1.0% + 5)	mq V, unit V, mqflags AC	40 Hz - 100 Hz
	4.000 V	1 mV		"	40 Hz - 400 Hz
	40.00 V	10 mV		"	"
	400.0 V	100 mV		"	"
	750 V	1 V		"	"
A=	4.000 mA	1 µA	±(0.8% + 3)	mq Curr., unit A, mqflags DC
	400.0 mA	100 µA	±(1.2% + 3)	"
	20.00 A	10 mA	±(2.0% + 5)	"
A≈	4.000 mA	10 µA	±(1.0% + 5)	mq Curr., unit A, mqflags AC
	400.0 mA	100 µA	±(1.5% + 5)	"
	20.00 A	10 mA	±(3.0% + 5)	"
Ω	400.0 Ω	100 mΩ		mq Res., unit Ω, mqflags -	Continuity beep < 50 Ω
	4.000 kΩ	1 Ω		"
	40.00 kΩ	10 Ω		"
	400.0 kΩ	100 Ω		"
	4.000 MΩ	1 kΩ		"
	40.00 MΩ	10 kΩ		"
Diode	2.000 V–	1 mV		mq V, unit V, mqflags DC,DIODE	Max. 1.5 mA
Data Hold				-
Frequency				-
Temperature				-

The column "sigrok result" contains in short form what the driver generates for the resp. data type.

The device seems to be extremely slow when the RS-232 interface is enabled and often takes up to about 10 seconds to detect a changed value or switch to another range. During this time a previous value keeps being sent. When changing to a new range automatically or manually, the device might send the old value scaled to the new range for a short time. This behaviour is caused by the device, not by sigrok! It improves slightly in manual range.