Accessories
Electronic Display Unit
In-/Outputs
Socket “Pulse Input
(For Wiring Diagram of the socket, refer to Point 8)
The pulses from the built-in Pulse Generator on the Gas Meter are read by the EDU via this analog input point. The required power supply (5 Volts) for the operation of the Pulse Generator is given out by this socket as well.
This power supply is given out via an internal resistor of 1 kOhm at the Pin “LED + and “LED GND. The power supply runs the LED of the Pulse Generator’s photo interrupter, or any connected electrical sensor designed to work with this voltage.
The two Pins “+ Darlington are two separate input channels for the pulses to be read in. Ritter Gas Meter Pulse Generators at present use only one input channel. A pulse is generated when one of these input channels is connected to GND. GND is the respective earth reference point. The input resistor has a value of about 20 kOhm when using the sensor types PG 2.0 and PG 3.0. When using the sensor type PG 2.0EX, the value of the input resistor is about 200 Ohm. The signals are shaped by the EDU via a Schmitt-Trigger. The lower trigger threshold value is about 1.5 Volts, and the upper trigger threshold value is about 3.5 Volts.
Socket “Analog Output
(For Wiring Diagram of the socket, refer to Point 8)
An Output Current signal (4 – 20 mA or 0 – 20 mA) and also an Output Voltage signal (0 – 1 Volt) can be transmitted via the round 5-pin “Analog Output socket at the back of the Unit. The values of these signals are proportional to the programmed measuring unit (refer to point 6.1/12) which is:
- the actual flow rate or
- the summarised volume
of the gas in the connected Gas Meter. To this socket can be connected, for example, an Analogue-Recorder, Regulator etc.
Output Current
The advantage of the Output Current is that the transmission of measurement signals can also occur over longer distances without being fundamentally influenced by outside disturbance.
For the respective measurable variable (Flow Rate/Volume), the following Minimum and Maximum Output signal values apply:
| Measurable variable | Corresponds to | ||
| Flow Rate [Ltr/h] | Volume [Ltr.] | Output Signal [mA] | |
| 0 | 0 | 0 oder 4 | |
| max. Flow Rate of the connected Gas Meter as given in its Data Sheet | max. Volume corresponding to the Programming according to Points 6.1/14 | 20 | |
The standard output signal is preset at 4 - 20 mA for the measurable variable "Flow Rate". To program the Output signal to 0 –20mA, see Point 6.1/11, to program the measurable variable, see Point 6.1/13.
The Current Interface is provided with a voltage of 24 V from within the Unit.
If the permissible current is exceeded by a malfunction within the EDU, the Unit switches the internal 24 Volt voltage off and the text "24 Volt" appears in the upper left-hand corner of the Display. At the same time, the green LED light at the back of the EDU 32 FP goes out and the internal Beeper gives off a continuous tone. After about 3 seconds, the Unit checks whether the overload is still present. If it is still present, the EDU 32 FP switches the Current Interface off again; after a short disconnection of the Display, the text "24 Volt" appears in the Display again and the continuous Beeper tone is given off again.
As the Current Interface output is short circuit proof and current limited, this announcement indicates that there is an internal error in the Unit.
Output Voltage
In order to activate the Output Voltage as Analog Output, the Current Output has to be switched off. The Selection/Programming is made via the Setup-Menu (Point 6.1/10: "Selection of Output Current or Output Voltage" refers).
The impedance of the Output Voltage Port is about 3 kOhm. Connected recorders or similar instruments should therefore have an input impedance of 10 kOhm or more, in order to avoid influencing the Voltage value.
For the respective measurable variable (Flow Rate/Volume), the following Minimum and Maximum Output signal values apply:
| Measurable variable | Corresponds to | ||
| Flow Rate [Ltr/h] | Volume [Ltr.] | Output Signal [mA] | |
| 0 | 0 | 0 | |
| max. Flow Rate of the connected Gas Meter as given in its Data Sheet | max. Volume corresponding to the Programming according to Points 6.1/14 | 1 | |
Time delay in the output of Flow Rate
The length of the intervals between the pulses is measured for the calculation of the flow rate. This means that a change in the flow rate has an immediate influence on the Voltage and Current Output values. If no pulse is measured for longer than 10 seconds, the flow rate is calculated as “Zero. Because the Analog values are generated over a 16-bit pulse-width modulation, the level has to be given out over a so-called “Integrator. This Integrator reacts with a short delay within seconds and also dependant upon whether the calculation Mode is set to "Arithmetic" or "e-Function" (smoothing).
The higher the maximum pulse frequency is, the faster the output can react to changes.
Examples when set to "arithmetic" Mode:
- TG 05 max. Frequency 1.6666 Hz for a pulse generator with 50 Pulses/Drum Revolution
-> Reaction time from 0 mA – 20 mA about 65 seconds. - BG 100 – max. Frequency 88 Hz for a pulse generator with 200 Pulses/Drum Revolution
-> Reaction time from 0 mA – 20 mA about 7 seconds.
The times in the examples correspond to a spring function, this means that the Gas Meters spring from not moving at all to the highest flow rate or alternatively that it suddenly ceases to move from the highest flow rate. This does not reflect reality. The data provided in the examples therefore symbolically indicate the maximum possible leading and trailing edges of the signal in relation to the maximum counting frequency. As the change in the Analog Output level is immediately readjusted with the change in the flow rate, only high springs in the flow rate can lead to a short delay in the output of the Analog values.
Signal-Overflow from too high a Flow Rate
When the connected Gas Meter type is selected on the EDU, the maximum flow rate according to the Data Sheet for that Meter will be automatically defined as such. For customer-made Gas Meters, the appropriate maximum flow rate can be programmed in (see Point 6).
If the connected Gas Meter is operated with a flow rate that is higher than the maximum indicated for it in its Data Sheet, the Output signal will remain constant once it reaches its maximum value. This means that for any overrun of flow rate, the Output Voltage will have a constant value of 1 Volt (when programmed to Output Voltage Signal), and the Output Current will have a constant value of 20 mA (when programmed to Output Current Signal).
Interface RS 232
(For Wiring Diagram, refer to Point 8)
The Display Unit can be connected to a Computer using the Interface RS 232.
For doing so the data transmission cable must be a cable with nine leads and with nine-pole terminals on both ends. All used leads between plug and socket of the cable are connected directly with each other, i. e. pin 2 of the plug is connected with pin 2 of the socket, pin 3 with pin 3 and so on. The pins/leads used for the data transmission are listed in point 7.3.1.
Interface Description:
| Sub-D-9-Socket: | Pin 2 = TxD | Transmitted Data |
| Pin 3 = RxD | Received Data | |
| Pin 4 = DTR | Data Terminal Ready (for Hardware-Handshake) | |
| Pin 5 = GND | Ground | |
| Pin 6 = RTS | Request To Send (for Hardware-Handshake) | |
| Signal Voltage: | +/- 15 Volts | |
| Data Transmission: | 9600 Baud, Data = 8 Bit, Parity = N, Stopbit = 1 | |
All of the data which are indicated in the Display can be transmitted to a Computer. In order to receive data, a Computer Program must send Control-Codes to the Interface. The Control Codes and the corresponding data are listed in Point 7.3.2.
Control-Codes:
| Ctrl-V | Hex 16 | provides: | VOL 00000,00 LTR (List of Decimals see Point 4, Table 1 & 2) |
| Ctrl-F | Hex 06 | provides: | FLOW 000,00 L/H (List of Decimals see Point 4, Table 1 & 2) |
| Ctrl-C | Hex 03 | causes: | RESET |
| Ctrl-T | Hex 14 | provides: | Type + Power Status |
| e.g. : | TG 05 Battery | ||
| TG 10 Mains | |||
| TG 20 Low Batt etc. |
The Interface will only send data when it has received a Control-Code. The text will be written in either English or German, depending on which language it has been programmed for use.
Use of the Control-Code "Ctrl-C" resets the Unit in the same way as pressing the RESET Key: All internal registers (counters) are set to zero, the programmed Set-up Values are then read, the Initial Announcement appears in the Display, followed by the Display Mode 1 values (refer to Point 4: "Display Modes").
Hardware-Handshake:
The adjustment of the Interface 232 to the connected Computer regarding the Hardware-Handshake is performed automatically. After receipt of a Control-Code (e.g. Ctrl-V for Volume), the Interface transmits the requested byte sequence (e.g. for Volume) as follows:
- When the connected Computer offers a Hardware-Handshake, that means, when the DTR signal is set to "High" at the reception site (i.e. the Computer), the Interface will set the RTS signal to "High", and will transmit information (in the form of a byte sequence) until the DTR signal is again set to "Low" by the Computer.
- When the connected Computer does not offer a Hardware-Handshake, that means when the DTR signal is not set to "High" within a defined time delay, the Interface will transmit the total byte sequence according to X-ON / X-OFF mode after that period of time has elapsed. The time delay equals the transmission time of a character at 9,600 Baud (= 0.8 msec).
Subject to alterations