DE4011858A1 - Liquid level measurement transducer - achieves fixed relationship between magnetic switches and defined values using shift register - Google Patents

Abstract

Several normally open switches (S2-S8) of magnetically neutral material are arranged in series along the measurement path in a protective tube. The switches are made contactlessly while a magnet moved by a float passes them. Each produces a characteristic signal. A digital measurement output is associated with the switches via a shift register (SR). The switches are connected to a common output line on one side and via diodes (D1-D8) to the shift register outputs on the other. USE/ADVANTAGE - Achieves fixed association of switches and defined measurement value outputs with relatively simple arrangement.

Description

The invention relates to a Liquid level transmitter with several in one Row along the measuring path in a protective tube arranged magnetically neutral material, normally open switches that go through one the protective tube or the switch row by means of Floating switching magnets one after the other for the duration of the comparison of the Switching magnets can be closed without contact, whereby in each position of the switching magnet at least one of the Switch is closed and each switch one certain measured value output is assigned.

A sensor of this type is for example from the CH-PS 5 75 591 known. The arranged in a row Switches lead there from a common measuring line individually and in their order on taps of a row of taps of a series resistor whose each tapped resistance value electrically into a analog measured value output is implemented.

The analog measurement method is not free from problems, because there are limits to the accuracy of measurement and the detectable measuring path length. The reasons are in the resistor series connection used, from which inevitably with increasing number of Resistance results in an error addition. Add to that the negative influence of the temperature drift, which is why with a Transmitter according to the known type of means for Zero point adjustment must be provided.

The invention has for its object a To design sensors of the generic type so that with relatively simple means a firm one Assignment of a specific measured value output to each Switch is reached.  

This object is achieved with the im Characteristic of the main claim specified characteristic solved. Further training of the Subject of the invention goes from the dependent claims forth.

The advantages achieved with the invention exist especially in that by means of the switches Digital measured value output assigned to the shift register always an error-free level display without previous Adjustment is achieved. Another advantage of Invention is to be seen in the fact that the connecting line between the transmitter and the evaluation without problems can be up to 100 m and more long.

Two embodiments of the invention are in the Drawing shown and are below described. Show it

Fig. 1 is a side view of a partially cut at the bottom of the liquid level transmitter,

Fig. 2 shows the circuit diagram of a Meßwertgeberelektronik with 8-stage shift register,

Fig. 3 is a simplified diagram of a Meßwertgeberelektronik with three series-connected 8-stage shift registers,

Fig. 4 shows the circuit diagram of a transmitter electronics with 4-stage shift register, which is combined with a flip-flop to form a basic unit and

Fig. 5 is a simplified diagram of a Meßwertgeberelektronik with three to a base unit of FIG. 4 are connected in series 8-stage shift registers.

The liquid level sensor shown in Fig. 1 consists essentially of several, normally open switches 5 arranged in a row along the measuring path in a protective tube 1 made of magnetically neutral material, which are switched by a switching magnet (not shown ) which can be moved along the protective tube 1 by means of a float 2 ) can be closed in succession without contact for the duration of the comparison of the switching magnet. The protective tube 1 is closed at the lower end with a plug 3 and has a mounting flange 4 at the upper end.

. The Meßwertgeberelektronik shown in Figure 2 consists in the embodiment shown here, in the smallest unit of an 8-stage shift register SR with 8, through diodes D ₁ - D ₈ decoupled reed switches S ₁ - S _8. The reed switches are here at a distance of 10 mm from each other, so that a level difference of 70 mm could be evaluated with this arrangement. The following relationship applies when several measurement electronics units are lined up:

Level difference (mm) = (register × 80) -10.

There are any number of electronic units can be used in series. your connection for evaluation takes place via a 6-core cable following lines:

1.Uv , supply voltage (5-12 volts DC)
2. GND , ground (common for supply and logic signals)
3. RST , line for resetting the shift register
4. CLK , clock for the shift registers
5. SW 2 , output of the last shift register
6. SW 1 , common output of all reed switches

The following assignment applies to the switches S ₁- S ₂:
1. Switch → level 0 mm
2. Switch → level 10 mm
3. Switch → level 20 mm
etc.

The input of the shift register SR (switch 1-8) is connected to + Uv , ie there is a logic 1 at the input. The bridge shown there is only necessary for the first shift register, because the input of the second register is connected to the output of the first register (see Fig. 2). The further interconnection of the register inputs and outputs follows the same pattern. The output of the last register is the signal output SW 2 .

The query starts when the shift register is reset via the RST line (pulse, logical 1).

With the 1st clock pulse on the CLK line , the 1st switch can now be queried via the SW 1 line:

Line SW 1 = 1 → switch is set
Line SW 1 = 0 → switch is not set

If the switch is not set, the second switch is queried with the second clock pulse as described above, then with the third clock pulse the third switch, etc .; If no switch is found in the event of a fault, an error can be signaled together with the SW 2 output. The SW 2 line is set to 1 at the same time as the last switch is queried, which enables the total length of the sensor to be queried.

In the second exemplary embodiment of the invention shown in FIGS . 4 and 5, the transmitter electronics is designed in such a way that it enables the detection of errors and malfunctions in connection with a computer.

The transmitter electronics consists of a 4-stage shift register SR with 4 reed contacts coupled via diodes and a flip-flop FF combined basic units SRFF and further shift register units SR , each consisting of an 8-stage shift register with 8 decoupled ree Contacts exist.

If the basic unit SRFF is arranged in series with several shift registers SR , the following relationship applies:

Level difference (mm) = 30 + (number of SR × 80).

The shift register units SR can be used in any number. The connection to the evaluation point is made via a 6-core cable, the length of which can be 100 m and more.

Functional description

The electrical connection to the evaluation point is made with the following services (see Fig. 5):

1.Uv , supply voltage (5-12 volts DC)
2. GND , ground (common for supply and logic signals)
3. RST , line for resetting the shift register
4. CLK , clock for the shift registers
5. SW 2 , output of the last shift register
6. SW 1 , common output of all reed switches

The following assignment applies to the switches:
1. Switch → level 0 mm
2. Switch → level 10 mm
3. Switch → level 20 mm
etc.

The flip-flop is set with a pulse via "RST" before the start of the query, ie "1" appears at the input of the first shift register and all shift registers are reset.

With the 1st clock pulse on the "CLK" line , a "1" appears at the 1st output of the first shift register. The flip-flop is reset with this signal, ie a "0" appears at the input of the first shift register. The 1st switch is queried via "SW 1 ":

Line ' SW 1 ' = 1 → switch is set
Line ' SW 1 ' = 0 → switch is not set.

With the 2nd clock pulse on the "CLK" line , the "1" is shifted from the 1st output to the 2nd output, followed by zeros, so that only a "1" is shifted in the result. The second switch is now queried as described above.

With the 3rd clock pulse the 3rd switch, etc .; when the last switch is queried, a "1" appears on "SW 2 " at the same time.

Pushing a "1" through all registers allows in Connection to a computer recognizing errors and malfunctions:

• - Faulty ree switches (open / close)
• - Interruption of data and supply lines
• - Broken float

The total length of the sensor can be queried via the "SW 2 " data line.

Claims (5)

1. Liquid level sensor with several normally open switches arranged in a row along the measuring path in a protective tube made of magnetically neutral material, which are switched by a switching magnet that can be moved along the protective tube or the row of switches by means of a float, one after the other, for the duration of the comparison of the switching magnet are closable, with at least one of the switches being closed in each position of the switching magnet and each switch being assigned a specific measured value output, characterized in that the switches ( S ₁ - S _n ) are assigned a digital measured value output by means of a shift register (SR) . 2. Transducer according to claim 1, characterized in that the switches ( S ₁ - S _n ) are on the one hand on a common output line (SW 1 ) and on the other hand in each case via diodes ( D ₁ - D _n ) decoupled from the outputs (1- n ) of the shift register (SR) are connected. 3. Transmitter according to one of the preceding claims, characterized in that the shift register (SR) consists of a series of 8-stage shift registers (SR ₁ - SR _n ) connected in series. 4. Transducer according to claim 1 or 2, characterized in that the shift register (SR) is formed from a series of series-connected multi-stage shift registers, of which the first is a 4-stage shift register, which with a flip-flop to a basic unit (SRFF ) is combined and the other shift registers (SR ₂ - SR _n ) are 8-stage. 5. Transducer according to one of the preceding claims, characterized in that the distance between the switches ( S ₁ - S _n ) in their row is 10 mm from each other.