Product Apr. 25, 2017

Hioki Launches Photovoltaic System Bypass Diode Tester FT4310

Instrument is First in the World to Detect Open Faults in Operating Panels

April 23, 2017 – Nagano, Japan

Hioki is pleased to announce the launch of the Bypass Diode Tester FT4310 for Photovoltaic Systems.

The FT4310, which is designed to test bypass diodes in strings of crystalline photovoltaic cells, can be used to detect open and short-circuit faults in bypass diodes by string either in daylight or at night. The instrument is the first portable device capable of detecting bypass diode open faults in operating panels (without requiring the panels to be shielded from sunlight).

*Bypass diode: A component that routes generated current around photovoltaic cells that are unable to generate electricity.
*String: A group of photovoltaic modules that have been wired together in series so that they generate power collectively.

Development Background
Bypass diodes used in photovoltaic systems are important components that play both an economic role, by keeping power generation from decreasing, and a safety role, by limiting heating in cells that are unable to generate electricity and thereby preventing the worst-case scenario of fire. However, technicians have been largely unable to inspect these components due to the lack of a simple method for testing them for open faults. Hioki developed and launched the FT4310 in order to facilitate fast, simple discovery of such faults in an effort to increase the safety of installed photovoltaic systems.
Principal Applications
· Maintenance and management of photovoltaic systems
· Installation of photovoltaic systems

Key Features
1. Detect open faults in bypass diodes by string either at night or during daylight hours, without the need to shield panels from sunlight

By disconnecting the string being measured from the grid, technicians can use the FT4310 to detect photovoltaic strings with bypass diodes with that have experienced an open fault, and they can do so at the junction box and without any need to shield the panels from sunlight. In this way, they can quickly identify malfunctioning strings.

2. Measure bypass route resistance, including the string’s wiring resistance
Since the FT4310 can measure bypass route resistance, including the photovoltaic string’s wiring resistance, customers can detect inspect for diode degradation (in the form of increased resistance) as well as increases in the contact resistance of the connectors between modules.

3. Detect cluster losses and bypass diode short-circuits by means of a high-precision DC voltmeter
When a bypass diode suffers a short-circuit fault, the string’s output voltage decreases (by about 10 V) because the corresponding photovoltaic cells no longer contribute to electricity generation. Since it incorporates a high-precision DC voltmeter, the FT4310 can detect this 10 V difference, allowing it to detect cluster losses and bypass diode short-circuit faults.

*Cluster: A group of photovoltaic cells that have been connected in series; the smallest unit of photovoltaic system operation. A cluster’s bypass diodes are connected in parallel. Also known as a photovoltaic cluster, or PV cluster.


Established in 1935, HIOKI E.E. CORPORATION (TSE: 6866) has grown to become a world leader in providing  consistent delivery of test and measuring  instruments through advanced design, manufacturing, and sales and services. By offering over 200 main products characterized by safety and quality while meeting an expansive range of applications, we aim to contribute to the efficiency and value of our customers' work in research and development, production and electrical maintenance. HIOKI products and services are available around the world through our extensive network of subsidiaries and distributors. Information about HIOKI is available at

Hioki FT4310 Bypass Diode Tester