M-System’s MD7 Series are lightning and surge protectors for instrumentation signal, network and power supply. Housed in only 7-mm-wide ultra slim housings, 16 surge protectors lined side by side take only 110-millimeter wide space. With the height and depth similar to PLCs and remote I/Os, they are ideal to be installed in panels and cabinets together with these instruments.

Four poles of terminals are equipped on each of surge side and protected side, three for signal and one for shield. By adapting an independent set of shield terminals, floating and grounding can be selected in free combinations to suit users’ applications.

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.

The maximum discharge current capacity is as high as 20 kA for an impulse wave of 8/20 microseconds. The MD7 Series are tested according to IEC 61643-21 standard to be suitable for categories C1, C2 and D1. C1 category requires the surge protector to withstand 300 times of average induced surges, C2 to withstand 10 times of strong induced surges generated in a harsh environment without electromagnetic shielding. D1 category is tested by two direct hits.

EASY COMMISSIONING
The MD7 Series are designed for multi-point, ultra-high-density installation. DIN rail mounting/grounding and slanted terminal block help installation and wiring work in such tight space.

When the DIN rail is grounded at single point, surge protectors mounted on it are automatically connected to the earth. There is no need of cross-wiring individual module.

Thanks to the terminal blocks slightly slanted forward, access from the front side to the terminals is easy even after the protectors are mounted on the rail.

INDEPENDENT SHIELD TERMINAL
Floating and grounding modes are selectable in free combination between shield and signal, shield and ground.

In the floating mode, the shield is normally insulated from the signal and the ground by a discharge element. When an elevated potential is detected by a lightning surge, the discharge element is immediately activated to prevent discharge at an undesirable location.

In the grounding mode, the shield is normally connected via the signal line with a low potential difference of several to several tens of volts, and connected permanently to the ground.

Each installation or network protocol requires different earth grounding method, such like both-end grounding, single-end grounding, SG terminal connection (Figure 1). The MD7 Series provide the most suitable grounding type for each application. (Table 1)

Figure 1. MD7 Series function digram and wiring example.

LOOP DISCONNECT FUSE
The model MD7ST, designed specifically for 4-20 mA loop, is provided with fuses to disconnect a failed device from the power bus supplying multiple devices. When the device protected by the MD7ST fails in shortcircuit mode, the fuse separates it from the power bus and protects the entire system.

M-System’s surge protectors are designed and identified for specific sensors or devices. Not only the selection of discharge elements but also the disposition of discharge elements and wiring routes are carefully studied for the most effective protection for each sensor/device type. Needless to say, it is easy to choose for you. There is no need of finding/knowing appropriate protection level values. Presently available product line-up is indicated in Table 2. More varieties for three-wire transmitters, strain gauge, pulse generating sensors will be added in the future.

 

Table 1. Shield connection types.

Table 2. MD7 Series line-up.

TYPE SHIELD – SIGNAL SHIELD – EARTH APPLICATIONS FF Floating Floating • Standard type • To protect a device having isolation between Signal and Earth • When SHLD should be floating against the earth (single-end grounding). FG Floating Grounding • To protect a device having isolation between Signal and Earth • When SHLD should be grounded (single- or both-end grounding). GF Grounding Floating • To protect a device having isolation between Signal and Earth • When SHLD wire should be connected to SG terminal of the protected device (SHLD is not grounded to the earth). GG Grounding Grounding • To protect a device which does not have a good dielectric strength between Signal and Earth

MODEL APPLICATIONS MD7ST 4 to 20 mA loop MD7TC Thermocouple transmitter MD7RB RTD & RTD transmitter MD7PM Potentiometer & Pot. transmitter MD74R RS-422 / RS-485 MD7PA PROFIBUS-PA MD7DP DC power supply