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| Figure 1. MD7 Series Appearance |
1. MD7 Series Features
(1) Form factor
M-System’s MD7 Series are lightning and surge protectors for instrumentation signal, network and power supply. Figures 1 and 2 illustrate the MD7 Series’ outer appearance and external dimensions, respectively. Housed in only 7 mm wide ultra slim housings, and similar to the height and depth of PLCs and remote I/Os, they are ideal to be installed in panels and cabinets together with these controllers and other instrumentation.
• Front: Shows product model and tag name.
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| Figure 2. MD7 Series External Dimensions |
• Side: Shows terminal schematic.
• Connection terminals: Due to the terminal blocks being slightly slanted forward, access from the front to the terminals is easy, even after the protectors are mounted on DIN rail.
• DIN rail adapter: When the DIN rail is grounded at a single point, the surge protectors mounted on it are automatically connected to the earth. Thus eliminating the need of cross-wiring individual modules.
(2) High performance
The multi-stage protection combining discharge elements at the first stage and the series resistances and diodes ensures to limit the current flow.
| Table 1. MD7 Series Products | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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2. New Models
Table 1 lists the full series lineup. New models are indicated by the “NEW” mark.
(1) Non-polar type
The Lightning Surge Protector for Two-wire Signal Loop (model: MD72W) and Lightning Surge Protector for Three-wire Signal Loop (model: MD73W) are non-polar type surge protectors, allowing them to be used without concern for signal polarity and to accommodate AC waveform signals. The MD72W is available in 4 variations with maximum continuous operating voltages of 7, 16, 32, and 55V, enabling users to select the best model for the signals in use. M-System recommends using the Lightning Surge Protector for Standard Signal Line (model: MD7ST) when you wish to further reduce negative clamping voltage.
(2) Pulse signal use
Because PLCs and remote I/O devices often use a large number of signals (configurations with 16 or 32 signals are common), protecting them requires a large number of surge protectors. The Lightning Surge Protector for Pulse Signal (model: MD7PL) can protect 2 pulse signals despite its 7 mm wide ultra-slim housing. Sixteen surge protectors mounted side by side are only 110 millimeter wide, and will protect 32 pulse signals.
The model is selectable using NPN (sink) or PNP connections (source) according to the I/O specifications of the protected device. Figure 3 provides an example of an NPN connection often used in Japan.
(3) Network use
Lightning Surge Protector for LONWORKS (model: MD7LWA) and the Lightning Surge Protector for FOUNDATION Fieldbus (model: MD7FB) have been newly added to the existing MD7 Series for RS-485 and PROFIBUS-PA.
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| Figure 3. MD7PL-Nxx Example Connection (NPN Connection) |
(4) Strain gauge use
The Lightning Surge Pro-tector for Strain Gauge (model: MD7LC) is available in an in-series connection type that enhances surge protection by connecting in-series resistors to the signal lines as well as a parallel connection type (without in-series resistors) that has little effect on signal lines. These variants can be selected based on a consideration of lightning strike frequency and strength.
(5) Future models
In the future M-System plans to introduce lightning surge protectors for low load current AC power supplies as well as models featuring the company’s popular service life monitor function.
 Click on the model numbers in Table 1. |