Abstract : This article focuses on the characteristics, typical application circuits, design methods, and application examples of photosensitive Z-elements and magnetic sensitive Z-elements, providing a reference for users developing applications using these elements. Keywords : Z-element, photosensitive Z-element, magnetic sensitive Z-element, sensor I. Introduction The photosensitive Z-element is one of the important varieties in the Z-semiconductor sensing element product series. It possesses similar current-voltage characteristics to the temperature-sensitive Z-element, and also features extremely simple application circuits, small size, large output amplitude, high sensitivity, low power consumption, and strong anti-interference capabilities. It can provide three output signals for users to choose from: analog, switching, and pulse frequency. Three-terminal digital sensors developed using it can communicate directly with computers without the need for preamplifiers, A/D, or V/F converters. The technical parameters of this element comply with the relevant provisions of QJ/HN002-1998. The magnetic sensitive Z-element is the third important variety in the Z-semiconductor sensing element product series. It possesses current-voltage characteristics similar to the temperature-sensitive Z-element. This element is small in size, has extremely simple application circuits, and can output analog signals, switching signals, and pulse frequency signals under the influence of a magnetic field. Furthermore, the output signal has a large amplitude, high sensitivity, and strong anti-interference capability. Photosensitive and magnetic Z-element elements and their three-terminal digital sensors can achieve the measurement, control, and alarm of physical parameters through the action of light and magnetism. II. Photosensitive Z-element and its technical parameters 1. Structure, circuit symbol, and naming method of photosensitive Z-element The photosensitive Z-element is a special PN junction formed through heavy doping. It is a two-terminal active element with asymmetrical positive and negative current-voltage characteristics. The marked or longer pin is the "+" terminal. 2. Current-voltage characteristic curve of photosensitive Z-element (d) is the current-voltage characteristic curve of the photosensitive Z-element. In the first quadrant, the OP segment M1 region is a high-resistance region (tens of kilohms to hundreds of kilohms). The pf segment M2 region is a negative-resistance region, and the fm segment M3 region is a low-resistance region (tens of kilohms to hundreds of kilohms). Where Vth is called the threshold voltage, it represents the maximum voltage across the Z-element at T (°C). Ith is called the threshold current, which is the current corresponding to Vth for the Z-element. Vf is called the conduction voltage, which is the minimum voltage in region M3. If is called the conduction current, which is the current corresponding to Vf, and also the minimum current in region M3. The third quadrant is the reverse characteristic. The reverse current IR is measured when the reverse voltage VR is 25V in the absence of light, and its value (microampere level) is very small. 3. Classification and Technical Parameters of Photosensitive Z-Elements The classification and technical parameters of photosensitive Z-elements are shown in Table 1. The classification codes are arranged according to the magnitude of the Vth value. There are two types of models, classified according to their response wavelength. Currently, the wavelength code for all products is 1. III. Photosensitive Characteristics of Photosensitive Z-Elements 1. 1. Measurement of the forward and reverse volt-ampere characteristics of a photosensitive Z-element in the absence of light: The photosensitive Z-element is covered with a light shield, i.e., its forward and reverse volt-ampere characteristics are measured by the measurement circuit under no-light conditions. The measurement circuit and method are the same as those for the temperature-sensitive Z-element. 2. Forward photosensitive characteristics of a photosensitive Z-element: The Z-element is connected to the forward characteristic measurement circuit and placed in a light field with variable illuminance. During measurement, the illuminance is increased from low to high in increments of 100 lx. A digital illuminance meter is used for calibration, and then the forward characteristics of the Z-element are measured, recording Vth, Ith, and Vf at different illuminance levels. The threshold point P(Vth, Ith) of the photosensitive Z-element moves to the upper left as the illuminance increases. The forward characteristics of the photosensitive Z-element also exhibit the photovoltaic phenomenon; the "positive" terminal of the Z-element is the "+" terminal of the photovoltaic effect. Currently, the saturation electromotive force of the photovoltaic effect is around 200 mV, and the short-circuit current increases with increasing light intensity. When the illuminance is 100 lx to 5000 lx, the short-circuit current is a few microamps to tens of microamps. 3. Reverse Photosensitive Characteristics of the Z-Element: Connect the Z-element to the reverse characteristic measurement circuit and place it in a variable light field. Change the illuminance of the light field, calibrate with a digital illuminance meter, and measure its reverse characteristics, i.e., the relationship between the reverse voltage VR and the reverse current IR. It can be seen that its reverse resistance decreases with increasing illuminance, while the reverse current increases with increasing light intensity. IV. Application Circuits of the Z-Element The Z-element has similar forward and reverse volt-ampere characteristics to the temperature-sensitive Z-element. Theoretically, the application circuits for the temperature-sensitive Z-element are also applicable to the Z-element. Considering that the Vth, Ith, and IR of the Z-element have a certain temperature drift, there should be a margin for temperature interference immunity in the optical switching circuit. In analog application circuits, an automatic temperature drift compensation circuit should be used. 1. The M1→M3 conversion circuit, outputting a negative step switch signal, operates in the absence of light. OP1 represents the characteristics of the photosensitive Z-element in region M1, with a threshold point of P1 (Vth1, Ith1). E is the power supply voltage. The straight line (E, E/RL), defined by the load resistance RL and the power supply voltage E, intersects the voltage axis (E) and the current axis (E/RL). Q1 is the operating point in the absence of light, with coordinates Q1 (VZ1, IZ1), and the output voltage VO1 = VZ1 = E - IZ1RL. We select appropriate circuit parameters so that when the illuminance is E2, the threshold point P1 moves to P2, exactly on the straight line (E, E/RL), at which point Q2 coincides with P2. The photosensitive Z-element then enters the negative resistance M2 region, and point Q2 reaches point f within a few microseconds, with coordinates f (Vf, If). At this point, the output voltage is VO2 = VOL = Vf, and a negative step switch signal is output. In order to obtain a negative step switch signal, when the illuminance is L2, the operating point Q2 coincides with the threshold point Vth2. The conditions that each parameter in the circuit must meet can be described by the following state equation: E＝Vth2＋Ith2RL （1） Wherein, the load resistance value RL is generally 1～2kW. The selection principle is that when the illuminance is L2, the Z-element works in the M3 region, the voltage of the operating point Q2 is VZ2＝Vf, the current is IZ2＝If, the product of voltage and current is VfIf＝P, and P≤PM≤50mW. That is, when the power consumption is not greater than 50mW, a smaller RL is selected. The amplitude of this switch signal is DVO: DVO＝Vth2-Vf （2） Formula (1) tells us the relationship between E, Vth2, and Ith2 in order to obtain a negative step switch signal. At this time, the following issues need to be considered: (1) The larger the illuminance L, the smaller Vth, the larger Ith, and the larger IthRL, the lower DVO will be, which may lead to the situation where the amplitude is too small to meet the requirements; on the other hand, excessive illuminance is also uneconomical. That is to say, the illuminance should be selected appropriately. (2) Within the scope of application, in the case of no light and no output of negative step switch signal, the working point Q1 should be selected as far to the right as possible, which is conducive to reducing the monitoring or alarm illuminance. (3) The DC power supply should be a low-power adjustable power supply. When monitoring or alarming illuminance L2, its value should be equal to the value calculated by formula (1). 2. Reverse application output analog voltage signal Z- element reverse current is extremely small, presenting a high resistance (1~6MW), this resistance has a negative illuminance coefficient, and does not break down under higher voltage (30~40V). Figure 5 is the reverse application circuit and working state analysis diagram. It can be seen that when there is no light, L1=0, the operating point is Q1(VZ1, IZ1), and the output voltage is VO1. Then: VO1=E-VZ1=E-IZ1RL (3) When the light is L2, the volt-ampere characteristic shifts upward, the operating point shifts from Q1 to Q2(VZ2, IZ2), and the output voltage is VO2. Then: VO2=E-VZ2=E-IZ2RL (4) 3. M1→M3, M3→M1 are mutually converted to output pulse frequency signal. This circuit only requires three components. A small capacitor is connected in parallel with the Z-element, and a load resistor RL is connected in series to form a light frequency converter, as shown in Figure 6. This achieves the purpose of using the photosensitive Z-element to realize the light control pulse frequency. Similar to the pulse frequency circuit of the temperature-sensitive Z-element, when there is no light, the power supply charges the capacitor through RL. When VC V. Summary of Photosensitive Z-Element Characteristics and Application Circuits The current-voltage characteristics of a photosensitive Z-element are extremely similar to those of a temperature-sensitive Z-element; the former's optical characteristics are also very similar to the latter's temperature characteristics. The characteristics and application circuits of a Z-element can be summarized as follows: There is a special point, the threshold point P(Vth, Ith), where the voltage sensitivity is negative and the current sensitivity is positive. There are two stable operating regions: the high-resistance M1 region and the low-resistance M3 region. At VZ... VI. Application Example of Photosensitive Z-Element 1. Temperature-Compensated Optical Switch Circuit This circuit uses two photosensitive Z-elements in reverse configuration, requiring that the reverse currents of the two Z-elements be equal and their reverse temperature sensitivity (DTR) be similar. V2 is shielded from light, and V1 is used under light. The current-voltage characteristics without light are V1 (0lx, T1℃) and V2 (0lx, T1℃). The current-voltage characteristics with temperature changes are V1 (0lx, T2℃) and V2 (0LX, T2℃). The current-voltage characteristic of V2 under light is V2 (Llx, T2℃). VR is the voltage across potentiometer R, VR1 (VR2) is the voltage across R at T1℃ (T2℃), and the output voltage VO is taken from half the resistance of R. In cases of slow temperature changes, VO is always equal to half the power supply voltage. Only when V2 is exposed to light does its reverse resistance decrease and IR increase. However, the current flowing through the three components in the series circuit of V1, R1, and V2 is equal, the potential at the midpoint of potentiometer R rises, and the output voltage VO2 increases. After reaching the set illuminance, the output of D1 changes from low to high, V3 conducts, and the relay contacts are activated to control other circuits. VII. Magnetic Z-Element and its Technical Parameters 1. Structure, Circuit Symbol, and Naming Method of Magnetic Z-Element A magnetic Z-element is a modified PN junction made through special doping. "+" indicates that it is connected to the "+" terminal of the power supply when used in the forward direction, and M indicates sensitivity to magnetic fields. 2. I-V Characteristic Curve of Magnetic Z-Element The volt-ampere characteristic of magnetic Z-element should be measured under conditions without a magnetic field. The volt-ampere characteristic measurement circuit and method are the same as those for the temperature-sensitive Z-element. In the volt-ampere characteristic, the OP segment is the high-resistance region, denoted as M1; the pf segment is the negative-resistance region, denoted as M2; and the fm segment is the low-resistance region, denoted as region M3. Vth in the characteristic is called the threshold voltage, representing the maximum voltage across the terminals at 25℃. Ith is called the threshold current, the current when the Z-element voltage is Vth. Vf is called the conduction voltage, the minimum voltage in region M3. If is called the conduction current, the current corresponding to Vf, the minimum current in the low-resistance region. The reverse characteristic has no magnetic sensitivity. 3. Classification and Technical Parameters of Magnetic Z-Elements The technical parameters of the magnetic Z-element are listed in Table 3. There are two classification codes for the magnetic Z-element: one is Vth, with four grades; the other is the threshold magnetic field, with two grades. The technical parameters of the magnetic Z-element conform to QJ/HN003-1998. VIII. Magnetic Sensing Characteristics of the Z-Element The forward volt-ampere characteristic of the Z-Element can be measured using the same circuit and method as that of the temperature-sensitive Z-Element. The shape of the volt-ampere characteristic curve of the Z-Element changes in a magnetic field, thus altering its technical parameters. The range of parameter changes as the magnetic field strengthens is shown in Table 3. 1. Threshold Magnetic Field: Bth (mT) The Z-Element is placed in a magnetic field, as shown in Figure 10. Self-excited oscillation is generated in the circuit, and the waveform of the output signal VO is similar to the pulse frequency signal triggered by the falling edge of the temperature-sensitive Z-Element. The magnetic field that causes the Z-Element to just begin oscillating is defined as the threshold magnetic field, denoted by Bth. 2. Magnetic Field Range: B (mT) The magnetic field range represents the magnetic field that sustains the normal oscillation of the Z-Element, with a value of (1～1.5)Bth. 3. Frequency Range: f (Hz) The normal signal frequency range of the Z-Element in the magnetic field. 4. Frequency sensitivity: SF (Hz/mT) 5. Voltage sensitivity ST (mV/mT) In a magnetic field, the voltage Vf of a Z-element increases as it shifts to the right. The stronger the magnetic field, the greater the increase in Vf. The voltage sensitivity ST is equal to the ratio of the increment of the conduction voltage Vf (DVf) to the increment of the magnetic field (DB). In experiments, besides the parameters mentioned above describing the changes in a magnetic field, there is another characteristic of the Z-element in a magnetic field that cannot be represented by corresponding parameters. For example, in a magnetic field, Vf increases in a stepwise manner, and Vth also increases simultaneously, with the amplitude change being: Vf: (1～3) Vf, Vth: Vth+(0～1V). This characteristic is very suitable for making magnetic switches, tachometers, etc. IX. Application Circuits of Z-Elements The Z-element is a nonlinear element. A typical application circuit is a circuit in series between the Z-element and a load resistor RL. One function of RL is to limit the operating current; another function is to extract the output signal from the connection point between RL and the Z-element. The Z-element allows a capacitor to be connected in parallel to output a pulse frequency signal. 1. The operating region of the magnetic Z-element, which outputs a step signal in region M3, depends on the magnitude of the power supply voltage E. During the transition from region M1 to region M3, the power supply voltage E, the load resistance RL, and the parameters Vth and Ith of the Z-element must satisfy the following condition-state equation: E = Vth + IthRL (7) This equation still applies to the magnetic Z-element. To ensure that the Z-element operates in region M3, the point P(Vth, Ith) must be set to the left of the load line (E, E/RL), and the influence of temperature should be considered. Within the applicable temperature range, it can reliably operate in region M3. As can be seen from the analytical diagram, the operating point is Q1(Vf, IZ1) when there is no magnetic field, and the output is VO = VOL = Vf. When a 300mT magnetic field is applied, P1 (Vth1, Ith1) moves to P2 (Vth2, Ith2), with P2 to the left of the line (E, E/RL). Q2 (VZ2, IZ2) is on OP2. The output at this point is: VO = VOH = E - IZ2RL. When the magnetic field B = 0, VO returns to a low level, i.e., VO = VOL = Vf. 2. Parallel capacitors M1→M3 and M3→M1 mutually convert the output pulse frequency signal. The self-excited oscillation generated by the Z-element in the magnetic field often has an unstable pulse frequency signal. Therefore, the method of parallel capacitors for the Z-element is used to improve the stability of the oscillation and the adaptability of the power supply voltage. This pulse frequency signal is triggered by the falling edge, and its frequency is modulated by the magnetic field. The application of the magnetic Z-element can involve interchanged positions of the Z-element and RL. Its output signal is a complementary signal with respect to the power supply voltage E. Referring to Table 4-3, the absolute values ​​of the signal amplitude changes, |DVO|, are equal. The former output signal rises from a low level to a high level, while the latter output signal falls from a high level to a low level. X. Summary of Magnetic Z-element Characteristics and Application Circuits The magnetic Z-element is sensitive to magnetic fields in the forward direction and has no magnetic sensitivity in the reverse direction. In its threshold point P(Vth, Ith), Vth is a positive magnetic coefficient, and Ith has a small negative magnetic coefficient. The magnetic Z-element also has two stable operating states: when VZ ≥ Vth, it operates in the low-resistance M3 region; when VZ ≥ Vth, it operates in the low-resistance M3 region. XI. Example of Magnetic Z-element Application 1. Flow Pulse Sensor This flow sensor is a circuit in which RL and a magnetic Z-element are connected in series. The Z-element operates in the M3 region, and the power supply voltage E should be greater than (Vth + IthRL) to ensure reliable operation in the M3 region within the allowable operating temperature range. A parallel magnetic field composed of N and S magnetic poles is fixed on a rotating disk. When the fluid impacts the rotating disk, a high-level signal VOH is output only for the instant the magnetic poles cover the magnetic sensitive Z-element. When the magnetic poles leave, the output is a low-level signal VOL. The number of magnetic pole pairs on the rotating disk is selected according to actual needs. The interval tx between the two high-level signals is a function of the flow rate. After calibration, a lookup table program can be programmed for display using a low-power microcontroller, and corresponding signals need to be output. The contact-type conical shaft of the tachometer is fixed to the magnetic poles. When the magnetic poles are rotated together by the conical shaft, the magnetic sensitive Z-element outputs the same signal as in Figure 14 under the action of the magnetic poles for counting and display. When N=1 and S=1, the number of magnetic pole pairs is P=1, the gate signal of the counter is t, and the counting is direct, displaying the rotational speed n [r/s] t=1/p (s) 2. The alarm sensor uses the circuit shown in Figure 15. The standby (safe state) level is high, VOH = E - IZ²RL. The protected item (valuable artifacts, appliances, doors, windows, etc.) is cleverly fixed to the magnetic pole, covering the magnetic Z-element. The output signal VOH indicates normal standby, i.e., the safe state. When the protected item is illegally moved, causing the magnetic pole to separate from the Z-element, the output signal changes from VOH to VOL, indicating an alarm has occurred. Using the VOL signal to trigger the alarm device, emitting an audible and visual alarm signal, or automatically triggering and sending a special remote alarm for assistance, are all technically very easy to implement. The magnetic Z-element can achieve many applications with simple circuits; there are many application examples, which will not be elaborated here. XI. Problems in the Research of Magnetic Z-Elements We have done a lot of work exploring the working mechanism and characteristics of magnetic Z-elements, but there are still many problems that need further investigation: 1. The highest sensitivity is achieved when the magnetic field lines are perpendicular to the normal to the plane of the Z-element core. However, the phenomenon that the sensitivity differs before and after the magnetic field direction changes remains unsolved. 2. The increase in Vf from weak to strong magnetic field exhibits abrupt changes, which limits the use of this Z-element for continuous measurements. 3. Magnetic Z-element typically has a large Vth (>10V), while those with a smaller Vth (<10V) often have lower sensitivity. Developing a magnetic Z-element with small Vth, high sensitivity, and low temperature drift is a new, high-investment, high-risk, and high-tech research project. The Z-element is a completely new type of element. Whether it's temperature-sensitive, light-sensitive, magnetic-sensitive, or force-sensitive, further improving its sensitivity, consistency, and stability presents a new challenge for us. We welcome colleagues and experts in the industry to work together to usher in a new era of Z-element research.