This document outlines the calibration procedures for the TT-SI 9001 and TT-SI 9002 devices, focusing on offset, low frequency CMRR, square wave, high frequency CMRR, and accuracy adjustments. The guide begins by detailing the various adjustment points on the device, providing a clear explanation of each component's function.

Function Description

The TT-SI 9001 and TT-SI 9002 are devices that require precise calibration to ensure accurate measurements. The calibration process involves adjusting several internal components, including variable resistors and capacitors, to achieve optimal performance. The device features a switch (SW1) for selecting attenuation ratios, allowing for different measurement ranges. A power switch (SW2) controls the device's operation, and an LED indicator confirms that the unit is powered on.

Key adjustment points and their functions are:

SW1 (Switch for selecting attenuation ratio): This switch allows the user to select the desired attenuation setting, such as 1/10, 1/20, 1/100, or 1/200, depending on the measurement requirements.
SW2 (Power switch): This switch turns the device on or off. When turned on, an LED indicator illuminates.
VR4 (Variable resistor for adjusting offset): This resistor is used to fine-tune the offset voltage, ensuring that the output is zero when no input signal is present.
VR2 (Variable resistor for adjusting offset): Similar to VR4, this resistor also contributes to offset adjustment, working in conjunction with VR4 to achieve precise zeroing.
VR1 (Variable resistor for adjusting low frequency CMRR): This resistor is adjusted to minimize common-mode rejection ratio (CMRR) at low frequencies, improving the device's ability to reject common-mode noise.
VR3 (Variable resistor for adjusting accuracy): This resistor is used to calibrate the overall accuracy of the device, ensuring that its output corresponds correctly to the input signal.
VC1 (Variable capacitor for adjusting square wave compensation): This capacitor is adjusted to optimize the device's response to square wave signals, ensuring accurate waveform reproduction.
VC2 (Variable capacitor for adjusting square wave compensation): Similar to VC1, this capacitor also aids in square wave compensation, working to maintain signal integrity for square wave inputs.
CON1 (Power jack for connecting to 6VDC power adapter): This is the input port for the external power supply, providing the necessary 6VDC to operate the device.

Usage Features

The device is designed for use with external measurement equipment such as a Digital Multimeter (DMM) and an oscilloscope. The input lines (black and red) are used to connect to the signal source, while the BNC connector output is used to connect to the DMM or oscilloscope.

To begin using the device, a 6VDC power adapter must be connected to CON1. Once powered on, the LED indicator should light up. It is recommended to warm up the unit for 10 minutes before starting any calibration procedures to ensure stable operation.

The calibration process involves several steps, each requiring specific connections and adjustments:

Offset Adjustment:

Shorting Input Lines: Both input lines (black and red) are connected together, effectively shorting them. This ensures a zero input signal for offset calibration. An alligator clip can be used for this purpose.
Connecting to DMM: The BNC connector output is connected to a DMM, which should be set to the mV range, preferably with auto-range capability.
SW1 Setting: SW1 is set to 1/10 (or 1/20) attenuation.
Adjusting VR2: VR2 is adjusted using a ceramic screw or appropriate tool to bring the output voltage as close to zero as possible (within 0.1mV).
SW1 Setting (Second Attenuation): SW1 is then set to 1/100 (or 1/200) attenuation.
Adjusting VR4: VR4 is adjusted to bring the output voltage to zero (within 0.1mV).
Iterative Adjustment: Since adjusting VR4 affects the 1/10 attenuation offset, steps 3 and 4 must be repeated. Similarly, steps 5 and 6 are repeated for the 1/100 attenuation. This iterative process minimizes the offset for both attenuation settings until it is ideally zero or within 0.1mV.

Low Frequency CMRR Adjustment:

Connecting to Oscilloscope: The output BNC is connected to an oscilloscope with good grounding.
Connecting to Power Source: Both input lines are connected to a 220/200VAC, 60/50Hz power source.
SW1 Setting: SW1 is set to 1/10 (or 1/20).
Oscilloscope Settings: The oscilloscope's VOLTS/DIV switch is set to 1mV, and the TIME/DIV switch to 5ms. A 60/50Hz sinusoid waveform should be displayed.
Adjusting VR1: VR1 is adjusted to minimize the amplitude of the displayed waveform, aiming for less than 1.5mV.

Square Wave Adjustment:

Connecting to Oscilloscope: The output BNC is connected to an oscilloscope with good grounding.
Connecting to Signal Source (Red Input): The red input line is connected to a 20Vp-p, 10KHz square wave signal source, and the black input line to ground.
SW1 Setting: SW1 is set to 1/10 (or 1/20).
Oscilloscope Settings: The oscilloscope's VOLTS/DIV switch is set to 0.1V for 1/10 (or 1/20) attenuation, and the TIME/DIV switch to 20us.
Adjusting VC1: VC1 is adjusted to make the displayed waveform match the ideal square wave shape.
Connecting to Signal Source (Black Input): The black input line is then connected to the 20Vp-p, 10KHz square wave signal source, and the red input line to ground.
Adjusting VC2: VC2 is adjusted to make the displayed waveform match the ideal square wave shape.
Repeat Adjustments: Steps for VC1 and VC2 adjustments are repeated until both adjustments are satisfactory.

High Frequency CMRR Adjustment:

Connecting to Oscilloscope: The output BNC is connected to an oscilloscope with good grounding.
Connecting to Signal Source: Both input lines are connected to a 155Vp-p, 20KHz sine wave signal source.
SW1 Setting: SW1 is set to 1/10 (or 1/20).
Oscilloscope Settings: The oscilloscope's VOLTS/DIV switch is set to 1mV, and the TIME/DIV switch to 0.1ms.
Adjusting VC1: VC1 is slightly adjusted to minimize the amplitude of the displayed waveform, aiming for less than 2mV.

Accuracy Adjustment:

Connecting to DMM: The output BNC is connected to a DMM.
Connecting to DC Voltage Source: The red input line is connected to the positive terminal of a 70VDC voltage source, and the black input line to the negative terminal of the same 70VDC source.
SW1 Setting: SW1 is set to 1/10 (or 1/20).
Adjusting VR3: VR3 is adjusted to make the output voltage equal to 6.9V (or 3.51V for 1/20).

Maintenance Features

The manual provides detailed instructions on how to open the device's case for maintenance and calibration. This involves a series of steps to carefully disassemble the unit without causing damage.

Opening the Case:

Remove Battery Lid: The first step is to remove the battery lid.
Loosen Screws: Two screws will be visible and need to be loosened.
Push and Pull Mortises: Near the BNC cable side, there are two protuberant mortises. These need to be pushed back and pulled upward to release the case.
Press and Pull Bottom Case: The bottom case needs to be pressed inward and then pulled backward and upward.
Push Back Bottom Case: Hold the bottom case and push it back in the direction of the input lines.
Remove Metal Cases: After these steps, two metal cases will be visible. There is one screw on the PCB that needs to be loosened to remove the entire metal case. Two wires will remain connected to the upper case and should be left in place.

These instructions ensure that the device can be safely opened to access the internal components for calibration and any necessary repairs or maintenance. The clear diagrams accompanying the text further aid in understanding the disassembly process. The emphasis on careful handling during disassembly highlights the precision required for maintaining the device's integrity.

Testec SI-9001 - Accuracy Adjustment Procedure

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