Volume flow meter / process control

Besides their built-in digital remote query capabilities (also see the RS232C interface) our measuring devices offer optional, intelligent analog interfaces (4..20 mA, 0..20 mA and 0..1 V, potential free ground), which are fully software configurable. A programmable threshold mode may be selected in order to use the interfaces as switching outputs, too, which enables quite a number of additional uses.

Left: comfortable configuration of the analog interfaces using a PC

It is possible to select any measured value to appear as analog output at the interface, i.e. volume flow, either pressure standardized or density standardized, line pressure, temperature, air density, total consumption. Besides one can choose a free physical unit for the measured value, such as l/min, l/s, m³/h, m³/s for volume flow, bar, kPa, PSI for gauge pressure, °C, °F for temperature, kg/m³ for air density and m³ for consumption. Finally any numerical limit for the range of measurement values can be entered, i.e. one can determine which measured value should lead to the maximum output signal (20 mA or 1 V).

The actual settings of the analog interface are shown in the display after the middle key of the VSM-02 is pressed (see also display). The interface can be configured to automatically generate zero and maximum levels each time the status display is invoked. Both signals will appear for approx. 0.5 seconds at the outputs. This is very useful for adjusting external analog equipment.

In threshold mode / switching mode the analog interface acts digitally, so to say. The output signal is either on minimum level (if the measured value is smaller than the programmed threshold value) or it is on maximum level (if the threshold value is reached or exceeded).

With little external circuitry (see examples above) the VSM-02 can therefore be used to directly switch other devices or machines. Switching alarm lamps, magnetic valves or compressors on or off as soon as a threshold value is reached imposes no problems. The output signal can also be made TTL-compatible, e.g. to send it to a separate process control unit.

RS232C with open query instructions

With our new RS232C interface module the VSM-02 and the VSM-3K can be integrated in industrial applications in a much more versatile manner.

The now available open query instructions enable the VSM-02 to become part of almost any customer specific process automation system, regardless of the operating systems and/or hardware used there.

Besides, the unique monitoring and protocolling functions of a VSM-02 for the consumption of gases or compressed air can now be used perfectly independent from any given operating system (i.e., they can be used under Windows, Linux, OS/2, MacOS, AS/400, LabView etc.).

The measured values and informations about the used physical units are sent by the interface module in plain ASCII with fixed format and configurable decimal delimiter, thus making the subsequent system independent processing of the measured data a very easy task.

Implemented instruction set:

Rn₁n₂<CR>

Code values for n₁:

Pressure std. vol. flow	Density std. vol. flow	Line pressure
4	2	1

Code values for n₂:

Temperature	Density	Consumption counter
4	2	1

The instruction code is built by adding the code numbers of the measured values which the VSM-02 should return.

Examples:

R21<CR: queries the density standardized volume flow plus the consumption counter
R77<CR>: queries all measured values
R06<CR>: queries temperature and density
R07<CR>: queries temperature, density and consumption counter

The measured values are sent, similar to their appearance in the built-in display, with an 8-digit numerical value and an 8-character physical unit. Output formatting is performed according to the individual settings found in the VSM. Leading zeroes are added by default. Instruction code R84 configures a point (".") as decimal delimiter, code R85 chooses a comma (",").

Special characters like in "m³" are simplified to "m3". Quering the consumption counter will additionally return the value of the 10000 m3 overflow counter.

rn₁n₂<CR>

This modified instruction (with lower case "r") works in principle in the same way, but less verbose. It only returns the numerical values, separated by a semicolon. No explicit physical units are returned.

R80<CR>

Serial number of the VSM (8 characters) + firmware version (2 hex-digits)

R81<CR>

Serial number of the actually chosen nozzle (8 characters)

R82<CR>

Normalization temperature (8 characters with unit)

R83<CR>

Settings of the analog interface (2*8 characters)

R84<CR>

Use a point (".") as decimal delimiter (default)

R85<CR>

Use a comma (",") as decimal delimiter

All presently delivered devices are, as standard, equipped with this new interface. Additionally the interface module is separately available in order to upgrade older VSM-02 models (automatic device identification).

Process control