1. Introduction
The ST4100/ST4800 Digital LCD Clamp Ground Resistance Meter, also known as a circuit resistance tester, is designed for precise measurement of grounding resistance. This instrument features a modern black luxury screen design, displaying resistance and current simultaneously. It includes functions such as real-time clock, data storage, data access, alarm, and automatic shutdown. The device is robust, featuring a dustproof, moisture-proof structure, making it suitable for various applications in telecommunications, power, meteorology, machine rooms, oil fields, and electrical installations. It accurately detects ground resistance using microprocessor control and rapid filtering technology to minimize interference.
2. Safety Rules and Precautions
WARNING: To avoid electric shock or personal injury, read and strictly adhere to all safety rules and precautions before use.
- This instrument conforms to IEC61010 safety specifications.
- Do not use high-frequency signal generators near the instrument during measurement to avoid errors.
- Pay attention to all labeled text and symbols on the instrument body.
- Before use, ensure the instrument and accessories are in good condition.
- Before starting up, pull the trigger once or twice to ensure the jaw is fully closed.
- Do not measure in flammable environments; sparks may cause an explosion.
- When starting up, do not pull the trigger or clamp any wire.
- Test the object only after normal boot and when the "OL Ω" symbol is displayed.
- Avoid placing or storing the instrument in high temperature, high humidity, or direct sunlight for extended periods.
- Always turn off the instrument before replacing batteries.
- If the battery voltage symbol appears, replace the battery promptly to maintain measurement accuracy.
- Keep the jaw contact plane clean and avoid wiping with corrosive agents or coarse materials.
- When opening the trigger, avoid impacting the clamp table, especially the clamp joint surface.
- A slight sound from the clamp head during resistance measurement is normal. Distinguish this from the "du-du-du" alarm sound.
- Adhere to the specified measuring range and operating environment.
- The measured wire current must not exceed the instrument's upper volume limit.
- Only authorized personnel should operate, disassemble, calibrate, and maintain this instrument.
- If the instrument is damaged or unsafe, discontinue use immediately and seal it.
3. Instrument Structure and Display
3.1. Key Components:
- Binding Clip (Pliers): The main clamping mechanism.
- Clip Opening and Closing Trigger: Used to open and close the pliers.
- LCD Display Screen: Shows measurement readings, symbols, and settings.
- Power Switch: Turns the instrument on/off.
- AL (Alarm) Key: Activates/deactivates and sets alarm functions.
- MODE Key: Switches between measurement modes.
- HOLD Key: Locks the current display data.
- SET Key: Enters setting mode and confirms selections.
- MEM (Memory) Key: Accesses data storage and deletion functions.
- Check Loop 1Ω / 10Ω: Used for self-calibration with a calibration ring.
3.2. LCD Display Symbols:
- : Pincer open symbol.
- )): Alarm indicator symbol (flashes when value exceeds set alarm).
- AC/DC: AC/DC indicator symbol.
- MEM: Data store symbol (flashes when saving, solid when stored).
- HOLD: Data lock symbol.
- MR: Data access symbol (displayed when reviewing data).
- OL Ω: Measured resistance is beyond the upper limit.
- LO.01 Ω: Measured resistance is beyond the lower limit.
- OLA: Measured current is beyond the upper limit.
- NOISE: Interference signal detected (accuracy not guaranteed).
- : Low battery voltage symbol (replace battery).
- Er: Boot error symbol (jaw not closed or wire clamped during boot).
4. Setup
4.1. Battery Installation
The instrument requires 4 x AA dry batteries (not included). Ensure the instrument is turned off before installing or replacing batteries. Observe correct polarity. If the low battery symbol appears on the LCD, replace the batteries promptly to ensure accurate measurements.
4.2. Initial Checks
- Before powering on, ensure the clamp jaws are clean and close properly. Pull the trigger once or twice to confirm proper jaw closure.
- Do not pull the trigger or clamp any wire when starting up.
- Maintain a natural static state of the clamp table during startup; avoid turning it or applying external force to the jaws to ensure measurement accuracy.
5. Operating Instructions
5.1. Startup & Shutdown
Press the Power button to turn the instrument on. It will automatically calibrate and display "OL Ω", entering resistance measurement mode. If "Er" is displayed, check if the jaw is closed properly or if a wire was clamped during boot. To shut down, press the Power button again. The instrument will flash for 30 seconds before shutting down.
5.2. Resistance and Current Test
After successful boot and "OL Ω" display:
- Pull the trigger to open the jaw.
- Clamp the pending test loop.
- Read the resistance value on the display.
The instrument can measure resistance and grounding leakage simultaneously. Use the MODE key to switch between "resistance + current" and "resistance + clock" modes.
In "resistance + current" mode, the current value (e.g., "0.00 mA") is displayed in the lower right. In "resistance + clock" mode, the ground voltage value (e.g., "12:00") is displayed. The time will reset after battery replacement.
5.3. Clock and Shutdown Time Setting
After boot, long press the SET key to enter setting mode. The lower-left number sets the shutdown time (5, 10, 15, 20 minutes, or OFF). Use the HOLD key to cycle through options. The lower-right number sets the clock. Short press SET to switch between year, month, day, hour, and minute. Use MODE to select the digit, and MEM or AL to adjust the value. Long press SET to save and exit.
5.4. Alarm Setting
Short press the AL key to toggle the alarm function on/off. Long press AL to set the resistance or current alarm value. Short press HOLD to select the digit, and SET and MEM to adjust the value. Use MODE to switch alarm modes. Long press AL to save and exit. The instrument will flash the )) symbol and emit a "du-du-du" sound if the measured resistance exceeds the set alarm value.
5.5. Data Locking / Storage
After a stable measurement, short press the HOLD key to lock the current display data. The data is automatically saved, and the "MEM" symbol will flash and be numbered. If storage is full, "MEM" will flash. Short press HOLD again to exit lock mode. The "MEM" symbol flashes during storage, and "HOLD" indicates data lock.
5.6. Data Review / Deletion
After saving data, short press the MEM key to enter data access mode, indicated by the "MR" symbol. Use short presses of SET or AL to navigate through stored data one by one, or long press to jump by 10. Short press MEM again to exit. To delete data, long press MEM in data access mode, then short press AL to delete the current data, or SET to cancel deletion.
5.7. Backlight On and Off
On the test screen, short press the SET key to turn the backlight on. Press SET again to turn it off.
6. Field Application
The clamp meter can be used for various grounding systems. The basic principle involves measuring the circuit resistance, where the clamp table measures voltage (V) and current (I) to derive resistance (R = V/I).
6.1. Multi-Point Grounding System
For systems like transmission tower grounding or communication cable grounding, where multiple grounding bodies are connected by overhead ground wires, the clamp meter measures the equivalent resistance. From an engineering perspective, the mutual resistance (RO) can often be assumed to be zero, simplifying the measurement to the predicted grounding resistance (R1).
6.2. Finite-Point Grounding System
In systems with a small number (N > 2) of interconnected grounding bodies, the instrument can measure the resistance at each ground branch (R1T, R2T, etc.). Solving for individual grounding resistances (R1, R2, etc.) requires solving a system of nonlinear equations. Specialized software may be needed for accurate calculation in such cases.
6.3. Single Point Grounding System
The clamp meter cannot directly measure single-point grounding. However, a test line and a grounding pole can be used to create an artificial loop for testing.
Two-Points Method:
Find an independent grounding body (RB) near the tested grounding body (RA). Connect RA and RB with a test wire. The measured resistance (RT) will be the series value of RA, RB, and the test line resistance (RL). If RT is less than the allowable grounding resistance, both RA and RB are considered qualified.
Three-Points Method:
Find two independent grounding bodies (RB and RC) near the tested grounding body (RA).
- Step 1: Connect RA and RB with a test line and measure R1.
- Step 2: Connect RB and RC with a test line and measure R2.
- Step 3: Connect RC and RA with a test line and measure R3.
The grounding resistance of RA can be calculated as: RA = (R1 + R3 - R2) / 2. The resistances for RB and RC can then be derived: RB = R1 - RA, RC = R3 - RA.
7. Technical Specifications
| Feature | ST4100 | ST4800 |
|---|---|---|
| Resistance Range | 0.010~500Ω | 0.010~1200Ω |
| Current Range | --- | 0.00mA~20.0A |
| Functions | Grounding resistance test, loop resistance test, leakage current test | |
| Ambient Temperature & Humidity | 23℃±5℃, <75%RH | |
| Power Supply | DC 6V (4 x AA dry batteries) | |
| Measurement Method | Mutual Inductance | |
| Resistance Resolution | 0.001Ω | |
| Current Resolution | 0.01mA | |
| Jaw Size | 55mm × 32mm | |
| Clock Function | Yes | |
| Display Type | 4-bit LCD display, black screen design | |
| LCD Size | 46mm × 36mm | |
| Instrument Size (L×W×H) | 295mm × 85mm × 58mm | |
| Measurement Time | One per second | |
| Data Storage | 500 groups (MEM symbol indicates full storage) | |
| Data Access | MR symbol indicates when accessing data | |
| Overflow Display | OL symbol indicates overrange overflow | |
| Interference Test | Automatic identification of interference signals (NOISE symbol when high) | |
| Alarm Function | Alarm prompt when measured value exceeds set point | |
| Battery Voltage | Real-time display of battery level | |
| Automatic Shutdown | Configurable (5, 10, 15, 20 minutes, or OFF; default 5 minutes) | |
| Power Consumption | 115mA Max | |
| Weight (including battery) | 1180g | |
| Working Temperature & Humidity | -10℃~40℃; <80%RH | |
| Storage Temperature & Humidity | -20℃~60℃; <70%RH | |
| Insulation Resistance | ≥20MΩ (between circuit and housing 500V) | |
| Withstand Voltage | AC 3700V/rms (between circuit and housing) | |
| External Magnetic Field | <40A/m | |
| External Electric Field | <1V/m | |
| Safety Regulations | IEC61010-1 (CAT III 300V, CAT IV 150V, pollution degree 2); IEC61010-031; IEC61557-1 (earthing resistance) | |
8. Maintenance
- Cleaning: Keep the jaw contact plane clean. Do not use corrosive agents or coarse materials for cleaning.
- Battery Replacement: When the low battery indicator appears on the LCD, replace the 4 x AA dry batteries immediately. Always turn off the instrument before replacing batteries.
- Storage: Store the instrument in a dry, cool place, away from direct sunlight and extreme temperatures or humidity.
- Calibration: The instrument supports self-service calibration using a calibration ring (1Ω and 10Ω). If grounding values seem inconsistent, use the calibrator to check the clamp meter's functionality.
9. Troubleshooting
| Symptom/Error Code | Description | Action |
|---|---|---|
| (Pincer open symbol) | Jaw is open, or jaws are severely polluted. | Ensure jaws are fully closed. Clean jaw contact surfaces if necessary. |
| (Low battery symbol) | Battery power is too low; accuracy cannot be guaranteed. | Replace the batteries immediately. |
| OL Ω | Measured resistance is beyond the upper limit of the clamp table. | Ensure the measurement is within the specified range. |
| LO.01 Ω | Measured resistance is beyond the lower quantity limit of the clamp gauge. | Ensure the measurement is within the specified range. |
| OLA | Measured current is beyond the upper limit of the clamp gauge. | Ensure the measurement is within the specified range. |
| )) (Alarm symbol flashes) | Measured value exceeds the set alarm critical value. | Check alarm settings or re-evaluate the measurement. |
| NOISE | Interference current is high; accuracy cannot be guaranteed. | Relocate to an area with less electrical interference. |
| Er | Boot error (trigger pulled, clamp open, or wire clamped during boot). | Ensure jaws are closed and no wire is clamped during startup. Restart the instrument. |
10. User Tips
- For consistent and accurate readings, always ensure the clamp jaws are clean and fully closed before initiating a measurement.
- When performing measurements, ensure the instrument is stable and not subjected to external forces that could affect jaw closure.
11. Warranty and Support
The contents of this user manual are for informational purposes only and do not justify product usage for unintended purposes. The manufacturer is not responsible for any losses caused by improper use. The manufacturer reserves the right to modify the contents of this user manual without prior notice. For technical support or service inquiries, please contact your vendor or authorized service center.
12. Packing List
| Item | Quantity |
|---|---|
| ST-4100/ST4800 Digital Resistance Meter | 1 set |
| Calibration Ring (Check ring) | 1 pcs |
| User Manual | 1 pcs |
| Aluminum Box | 1 pcs |
13. Additional Resources
A detailed user manual in PDF format is available for download. This document provides further in-depth information and diagrams for advanced usage and reference.
Reference: User Manual (PDF)