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How to identify the advantages and disadvantages of voltage and current transducers
(1) When the primary side is overloaded, the output current does not exceed 25.000mA+10%, otherwise the 24V working power supply and A/D input clamping circuit used in the PLC/DCS for the transmitter are damaged due to excessive power consumption. The transmitter-to-output in the transmitter is also damaged due to excessive power consumption, and the A/D input clamp circuit is even more vulnerable.
(2) When the working voltage is 24V reversed, the transmitter must not be damaged and must have polarity protection;
(3) Whether or not the clamp voltage is detected when the induced surge voltage exceeds 24V: In the two-wire output port and an AC 50V pointer meter, use AC 50V to connect two wires to instantly touch the two-wire output port. Clamping, how many volts can be clamped at a glance;
(4) The identification of whether or not there is polarity protection: Use an analog multimeter to multiply the positive and negative of the 10K file to measure the two-wire output port. There is always an infinite resistance of Ω, and there is polarity protection;
(5) There is a long-term short-circuit protection of the electrodeless output current: when the primary input is 100% or when the overload is greater than 125%-200%, the load is short-circuited to 250Ω and the short-circuit protection limit is measured at 25mA+10%;
(6) Industrial level and civil commercial level discrimination: The industrial grade operating temperature range is -25 degrees to +70 degrees, the temperature drift coefficient is 100ppm per degree, that is, the temperature changes by 1 degree per degree, and the accuracy changes to one ten thousandth. Civilian commercial-grade operating temperature range is 0 degrees (or -10 degrees) to +70 degrees (or +50 degrees), temperature drift coefficient is 250ppm per degree, that is, temperature change per degree is 1 degree, precision changes to 10000 Two-fifth; temperature and voltage transmitter temperature drift coefficient can use the incubator or high and low temperature box to test more complex.
(7) When the voltage between the two lines due to induction lightning and induced surge voltage exceeds 24V, the transmitter must be clamped, and the transmitter must not be damaged; generally, 1-2 TVS transient protection diodes 1.5KE can be inhibited in parallel between two wires. The 20-millisecond pulse width of the positive and negative pulse of 20 seconds interval, the transient withstand impact power 1.5KW-3KW;
(8) The reference must be stable, 4mA is the corresponding input zero reference, the reference is unstable, and the linearity of the accuracy is not relevant. The zero offset of 4mA within 4 minutes of cold boot does not exceed 4.000mA0.5%; (ie, 3.98 -4.02mA), the pressure drop on the load 250Ω is 0.995-1.005V, the IC chip in foreign countries often uses the expensive energy gap reference, and the temperature drift coefficient varies by 10ppm per degree;
(9) The total current consumption of the internal circuit is <4mA, equals to 4.000mA after setting, and the active rectifier filter amplifies the constant current circuit, and the consumption current of the active current rectifying filter amplifies the constant current circuit also changes. The foreign IC chip adopts constant current power supply;
(10) When the working voltage is 24.000V, when the full scale is 20.000mA, the full-scale 20.000mA reading will not change due to the load 0-700Ω; the variation does not exceed 20.000mA0.5%;
(11) When the full-scale range is 20.000mA, when the load is 250Ω, the full-scale reading of 20.000mA will not change due to the change of the operating voltage 15.000V-30.000V; the change does not exceed 20.000mA0.5%;
(12) The linearity of the product marking 0.5% is the absolute error or the relative error, which can be discerned by the following method: At the same time, the following linearity is 0.5%. When the primary input is zero, the output is 4mA plus or minus 0.5. % (3.98-4.02mA) with a voltage drop of 0.995-1.005V at 250Ω
When the input of the primary side is 10%, the output is 5.6mA plus or minus 0.5% (5.572-5.628mA), and the load voltage at 250 ohms is 1.393-1.407V.
When the primary input is 25%, the output is 8mA plus or minus 0.5% (7.96-8.04mA), and the load voltage at 250Ω is 1.990-2.010V.
When the input voltage is 50% at the primary input, the output voltage is 12mA plus or minus 0.5% (11.94-12.06mA), and the load voltage at 250Ω is 2.985-3.015V.
When the primary input is 75%, the output is 16mA plus or minus 0.5% (15.92-16.08mA). The load is 250mA with a voltage drop of 3.980-4.020V.
When the primary input is 100%, the output voltage is 20mA plus or minus 0.5% (19.90-20.10mA). The pressure drop across the 250Ω load is 4.975-5.025V.
(13) When the primary input is overloaded, it must be current-limited: When the primary input overload is greater than 125%, the output over-current limit is 25mA+10% (25.00-27.50mA). The pressure drop on the load 250Ω is 6.250-6.875V;
The above 13 methods can also be used to distinguish between the true and false advantages and disadvantages of other transmitters.