After the marketization of the means of production, intensified fierce competition, which is difficult to discriminate between true and false, and because transmitters are marginal disciplines, many engineering designers are relatively unfamiliar with this, and some manufacturers' product industry levels and civilian commercial level indicators are confused (industry The price of the class is 2-3 times that of the civilian commercial grade.) Some manufacturers can use the LM324 and LM431 with a few cents to make a transmitter. If you don’t believe it, you can open it and you’ll buy it for a few hundred dollars. With the LM324 and LM431, such a transmitter to send you, you dare to use Oh!
Here try to use the commonly used 0.5 current accuracy voltage and voltage transmitter as an example, starting from the following methods to distinguish between true and false advantages and disadvantages.
(1) The reference should be stable, 4mA is the corresponding input zero reference, the reference is unstable, and the linearity of the accuracy is not good. The zero drift of 4mA within 3 minutes of the 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 changes by 10ppm per degree;
(2) The total consumption current of the internal circuit is less than 4mA, equals to 4.000mA after setting, and the active rectifier filter amplifies the constant current circuit, and the current consumption also changes due to the change of the primary input. The IC IC in foreign countries adopts constant current power supply;
(3) When the operating 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 change transmitter interference signal does not exceed 20.000mA0.5%;
(4) When the signal isolator is full-scale 20.000mA, when the load is 250Ω, the reading of full-scale 20.000mA will not change due to the change of the working voltage 15.000V-30.000V; the change does not exceed 20.000mA0.5%;
(5) 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.
(6) When the operating voltage of the instrument isolator in Shaoxing is reversed at 24V, the transmitter must not be damaged and must have polarity protection;
(7) When the voltage between the two lines due to induction lightning and induced surge voltage exceeds 24V, do not damage the transmitter; generally, connect 1-2 TVS transient protection diodes 1.5KE in parallel between the two lines to suppress each 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 linearity of the product labeling 0.5% is an absolute error or a relative error. It can be clearly identified by the following method: The following indicators are true linearity of 0.5%.
When the input is zero, the output is 4mA positive and negative 0.5% (3.98-4.02mA), the load voltage 250Ω is 0.995-1.005V The input is 10%, the output is 5.6mA positive and negative 0.5% (5.572-5.628mA) load 250 The drop in 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) Load The pressure drop on 250Ω is 1.990-2.010V When the primary input is 50%, the output is 12mA plus or minus 0.5% (11.94-12.06mA) Load 250Ω The pressure drop 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 250Ω and the voltage drop is 3.980-4.020V
The output is 20mA plus or minus 0.5% when the input is 100% on the primary side (19.90-20.10mA) The load pressure on the 250Ω is 4.975-5.025V
(9) 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;
(10) 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 the AC 50V to connect the two wires to instantly touch the two-wire output port. Clamping, how many volts can be clamped at a glance.
(11) Discrimination with or without polarity protection: Use an analog multimeter to multiply the 10K file positive and negative to measure the two-wire output port. There is always an infinite resistance of Ω, and there is polarity protection;
(12) 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 to be 25mA+10%;
(13) The discrimination between industrial grade and civil commercial grade: 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 by one 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, accuracy is changed to 10000 Two-fifth; temperature and voltage transmitter temperature drift coefficient can be used to test the incubator or high and low temperature box to verify the more cumbersome, Shaoxing instrument production of current and voltage transmitter accuracy of 0.2%.
The above 13 methods can also be used to distinguish between the true and false advantages and disadvantages of other transmitters.
Here try to use the commonly used 0.5 current accuracy voltage and voltage transmitter as an example, starting from the following methods to distinguish between true and false advantages and disadvantages.
(1) The reference should be stable, 4mA is the corresponding input zero reference, the reference is unstable, and the linearity of the accuracy is not good. The zero drift of 4mA within 3 minutes of the 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 changes by 10ppm per degree;
(2) The total consumption current of the internal circuit is less than 4mA, equals to 4.000mA after setting, and the active rectifier filter amplifies the constant current circuit, and the current consumption also changes due to the change of the primary input. The IC IC in foreign countries adopts constant current power supply;
(3) When the operating 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 change transmitter interference signal does not exceed 20.000mA0.5%;
(4) When the signal isolator is full-scale 20.000mA, when the load is 250Ω, the reading of full-scale 20.000mA will not change due to the change of the working voltage 15.000V-30.000V; the change does not exceed 20.000mA0.5%;
(5) 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.
(6) When the operating voltage of the instrument isolator in Shaoxing is reversed at 24V, the transmitter must not be damaged and must have polarity protection;
(7) When the voltage between the two lines due to induction lightning and induced surge voltage exceeds 24V, do not damage the transmitter; generally, connect 1-2 TVS transient protection diodes 1.5KE in parallel between the two lines to suppress each 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 linearity of the product labeling 0.5% is an absolute error or a relative error. It can be clearly identified by the following method: The following indicators are true linearity of 0.5%.
When the input is zero, the output is 4mA positive and negative 0.5% (3.98-4.02mA), the load voltage 250Ω is 0.995-1.005V The input is 10%, the output is 5.6mA positive and negative 0.5% (5.572-5.628mA) load 250 The drop in 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) Load The pressure drop on 250Ω is 1.990-2.010V When the primary input is 50%, the output is 12mA plus or minus 0.5% (11.94-12.06mA) Load 250Ω The pressure drop 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 250Ω and the voltage drop is 3.980-4.020V
The output is 20mA plus or minus 0.5% when the input is 100% on the primary side (19.90-20.10mA) The load pressure on the 250Ω is 4.975-5.025V
(9) 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;
(10) 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 the AC 50V to connect the two wires to instantly touch the two-wire output port. Clamping, how many volts can be clamped at a glance.
(11) Discrimination with or without polarity protection: Use an analog multimeter to multiply the 10K file positive and negative to measure the two-wire output port. There is always an infinite resistance of Ω, and there is polarity protection;
(12) 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 to be 25mA+10%;
(13) The discrimination between industrial grade and civil commercial grade: 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 by one 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, accuracy is changed to 10000 Two-fifth; temperature and voltage transmitter temperature drift coefficient can be used to test the incubator or high and low temperature box to verify the more cumbersome, Shaoxing instrument production of current and voltage transmitter accuracy of 0.2%.
The above 13 methods can also be used to distinguish between the true and false advantages and disadvantages of other transmitters.