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Remote transmission principle and application prospect of magnetic level gauge

Time: 2012-09-24 14:57:29 source: Author:

[foreword] in 2004, a new magnetic level gauge with remote output was installed in the No.1 ammonia evaporator of the refrigeration section. The model of local indicating instrument is uhz-25, which is a common magnetic turnover plate level gauge. It is intuitive and eye-catching, which is conducive to the reading of process personnel. The model of remote transmitter is lb. its principle and structure are novel, simple and reliable. The instrument has been put into operation for more than one month, and the operation is stable and reliable with satisfactory results.

The technical parameters of remote transmitter of liquid level gauge are as follows:

Principle of measurement reed resistance chain magnetic coupling
The measuring range is 300-8000mm
Accuracy (iomm)
Huichaishi 1 mm
Output signal 4-20mad, C (two wire system)
Load capacity 600 ohm, power consumption < 1.ow
Ambient temperature - 40 to + 80 ° C
Protection class IEC IP65
Supply voltage 14-40v D. C
Distance Max 10 km
Cable joint waterproof type m16x1.5 female thread flameproof type m20x 1.5 female thread
Explosion proof intrinsically safe IB iibt4 (to be used with Zener barrier)

Principle of liquid level transmitter

The LB type liquid level transmitter is composed of a liquid level sensor and a conversion module. The liquid level sensor is composed of a set of dry spring and resistance chain. The electrical connection between the reed J and the resistance R is shown in the figure

The reed and resistance should be set every 20 mm and installed in a stainless steel pipe at equal distance. The resistance values of all resistors are the same, that is: R1 = R2 = R3,... = RN. The number of resistances is determined by the level measurement range (i.e. the length of the scale). For example, when the measuring range is 1200mm, the number of R resistances is n = 1200 / 20 = 60 (pieces).

The liquid level sensor and the magnetic flap level gauge are installed in parallel on one side of the float, and are in the magnetic coupling system of the magnetic float. When the magnetic floater follower moves up and down with the liquid level, the reed tube corresponding to the height is pulled in by the magnetic field, which changes the resistance value Rab of the resistance chain shown in points a and B in Fig. 1. For example, when the liquid level is at a low position, Jo pulls in, and all resistances are short circuited by Jo, Rab is 0; when the liquid level is at a higher position, jn is pulled in, and Rab is the sum of N resistors in series. That is, Rab = 0 when the liquid level is 0%, and the Rab is larger when the liquid level is 100%.
The conversion module is actually a simple circuit for measuring resistance value, which is composed of Ω / V (resistance / voltage) conversion circuit, V / I (voltage / current) conversion circuit, zero position and range adjustment circuit. The block diagram is shown in Figure 2.

 Conversion circuit block diagram of remote transmitter of magnetic flap level gauge
After the signal of 20 mA, which is higher than that of the liquid level sensor D, the signal is processed by the resistance of the terminal A and B, which corresponds to the liquid level of the standard sensor.

More complete original pdf http://tealattewithstyle.com/xiazai/