Digital multimeter BM859s TRMS (AC+DC), dBm, T1, T2, USB/RS232 102019

Professional multimeter for special tasks in automation and power engineering

In environments requiring precision, such as diagnostics of industrial automation systems or analysis of power distribution networks, standard meters are often insufficient. The BM859s model is a device designed to solve complex measurement problems, offering True RMS for AC and AC+DC waveforms in a wide bandwidth up to 100 kHz. Thanks to this, it not only measures voltage and current but also correctly reads distorted signals, which is crucial when analyzing inverters or switching power supplies. The device stands out with high resolution – up to 50,000 counts in standard mode, and in DCV (DC voltage) measurement mode, it expands to 500,000 counts, allowing the detection of even minimal changes in circuits.

Safety and features protecting against operator errors

Working with high voltages requires not only good equipment but also mechanisms preventing human errors. This multimeter is equipped with the Beep-Jack™ system, which acoustically signals an attempt to connect leads to incorrect input jacks. This is a simple but effective function that significantly reduces the risk of damaging the device or creating an electric arc when measuring current instead of voltage. The construction meets rigorous safety standards: category CAT IV 600 V and CAT III 1000 V, making it a safe tool for work on main switchboards and industrial installations. High overvoltage protection (up to 8 kV) provides additional certainty during measurements in difficult environmental conditions.

Advanced diagnostics and data analysis

Beyond basic measurements (voltage up to 1000 V DC/AC, current up to 20 A AC/DC, resistance up to 50 MΩ), the device offers a range of analytical functions essential for service technicians:

• Temperature measurements: Two independent channels (T1, T2) allow simultaneous reading of temperature from -50°C to 1000°C and calculating the difference between them (T1-T2), which is useful, for example, when checking heat losses on heating elements or motors.
• Signal analysis: The CREST-MAX (PEAK HOLD) function records peak values lasting even 0.8 ms, and the MAX/MIN/AVG mode allows tracking parameter changes in real time without the need to constantly observe the display.
• Specialist applications: Built-in dBm attenuation measurement with the ability to select one of 20 impedances (from 4 to 1200 Ω) facilitates work in telecommunications and audio. The percentage function for the 4–20 mA current loop simplifies calibration of process sensors without the need for manual calculations.
• Communication: Data can be transmitted to a computer using an optional RS232/USB optical interface kit (KIT BRUA-85xa), enabling result archiving and further analysis on a desktop computer.

Readability and work ergonomics

The dual-type LCD display ensures readability even with dynamically changing signals thanks to fast bargraph refresh (60 times per second) and the main digital display (5 times per second). The HOLD function freezes the result on the screen in hard-to-reach mounting locations, and the relative measurement mode Δ facilitates comparing values with a baseline value. The meter is compact (dimensions approx. 198 x 97 x 55 mm) and relatively light (approx. 500 g), which facilitates moving it between workstations without burdening the technician's hands during long measurement sessions.

Key applications of this model's functions include precise measurement of inverter power supplies thanks to the True RMS AC+DC mode and quick visualization of peak value changes during motor startup using a bargraph with a 6 Hz refresh rate. Safety during work at main power switchboards is guaranteed by the high CAT IV category, while the RS232/USB interface allows for automation of data collection in control and measurement processes without the need to manually transcribe results. Additionally, the dBm function supports diagnostics of audio and telecommunication lines taking source impedance into account.