Sample Holder

Introduction

Sample Holder

A sampler is a switch circuit or device that takes out the value of the processed signal at a fixed point in time. The sample-and-hold device amplifies this signal value and stores it for a period of time for conversion by the analog-to-digital converter. It will take out an analog signal value to replace the original value until the next sampling time. During the operation of the analog-to-digital converter, the sample-and-hold device keeps the input value at the beginning of the conversion, which can suppress the conversion noise caused by amplifier interference, reduce the aperture time of the analog-to-digital converter, and improve the accuracy and accuracy of the analog-to-digital converter. Eliminate the inaccuracy of conversion time. The analog input of general production process control computer may be tens or hundreds of points per second. For large-scale systems or even thousands of points, high-speed sampling (such as 5000-10000 points/sec) is often required. In order to send these analog signals to the analog-to-digital converter one by one without reducing the authenticity of the signal under test, a sample-and-hold device must be used. In low-speed systems, such devices can generally be omitted.

Principle

The sample-and-hold circuit is composed of analog switches, storage elements and buffer amplifier A. At the sampling moment, the digital signal added to the analog switch is low level. At this time, the analog switch is turned on, so that the voltage UB across the storage element (usually a capacitor) changes with the sampled signal UA. When the sampling interval expires, D becomes a high level, the analog switch is disconnected, and UB remains unchanged at the moment of disconnection. The function of the buffer amplifier is to amplify the sampled signal. There are two basic types of connections in the circuit: one is to amplify the signal before storage, and the other is to store and then amplify. For an ideal sample-and-hold circuit, it is required that the switch has no offset and can move quickly with the control signal, and the impedance of the disconnection should be infinite. At the same time, it is also required that the voltage of the storage element can track the voltage of the analog signal without delay, and can be at any length Keep the value unchanged for the period of time.

Others

Usually, sample holders, samplers, amplifiers, and analog-to-digital converters form analog input channels for industrial process computer systems or data acquisition systems. Field signals (such as temperature, pressure, flow, level, mechanical quantity and component quantity and other measured parameters) are sent to the sampler after signal processing (scale conversion, signal isolation, signal filtering, etc.), and the signal is processed under the control of the controller Carry out time-sharing tour and multi-channel switching selection, and then send it to the analog-to-digital converter through the amplifier and sample-and-hold circuit, and convert it into binary digital that the computer can accept.