Safe-Guarding Mat Systems from Miller Edge
Miller Edge, Inc. Posted 11/24/2009
1. What is a Safe-Guarding Mat?
A Safe-Guarding Mat is a simple and convenient method of providing a safeguard for persons working within or near a dangerous piece of machinery. A Safe-Guarding Mat is a presence sensing safety device (PSSD) that detects the presence of someone or something within the protected area.
2. What are the physical characteristics of a Safe-Guarding Mat?
a) A Safe-Guarding Mat consists of two conductive Alumaglas plates that are held apart by non-conductive compressible foam separators. When the mat is activated the non-conductive separator compresses into their recesses allowing the two Alumaglas plates to make contact giving overall sensitivity to the mat surface.
b) The surface of the Safe-Guarding Mat is heavy-duty ribbed vinyl or diamond top for the maximum in anti-slip design. The mat is completely sealed and meets European Rating (IP-54) and it provides excellent protection from most chemicals and liquids. Washdowns are no problem.
c) Minimum weight with assured detection 30kg per 80mm diameter disk(66lbs. per 3 1/8” diameter disk)per EN-1760
d) Actual detection is 15-20lbs per 3 1/8” disk.
e) Maximum detection zone: 1000 square meters for multiple mat systems.
f) 4 wire "No Dead Zone" construction.
g) 10-Ton forklift truck capacity.
3. What is a Safe-Guarding Mat system?
A Safe-Guarding Mat system is comprised of a Safe-Guarding Mat or multiple mats and must be connected to a "Control Reliable" Safe-Guarding Mat controller. The controller must employ redundant positive-guided relay outputs. The mat and the controller must meet European Standard EN-1760-1 and Safety Category 3.
4. What standards apply for Safe-Guarding Mat systems?
a) United States
ANSI-B11.19 - 1990 ANSI/RIA-15.06 – 1999
b) European Union
EN-1760-1 EN-292
c) Class C Standards - Machine Specific
Miller Edge Safe-Guarding Mat systems are CE Approved to Safety Category 3.
5. What are the necessary features for Safe-Guarding Mat systems?
a) Complete coverage of hazardous area.
b) Mat must be permanently affixed to the floor.
c) Ramp trim to prevent tripping is required.
d) "No Dead Zones".
e) Remember safety distance calculation.
f) Four (4)-wire construction is required.
g) Safe-Guarding Mat must be used with a "control reliable" Safe-Guarding Mat controller. Response time shall be specified on the controller. The maximum response time must be less than 100ms over the system operating temperature range.
h) Mat must have a minimum object sensitivity, which detects 30-kg (66-lb.) weight on an 80-mm (3.125-inch) diameter circular disk anywhere on the mat sensing surface.
i) Safe-Guarding Mat system shall be installed and arranged such that the reset of the safety function requires removal of the obstruction from the sensing surface followed by a separateand deliberate action outside of the sensing surface, when used as the sole means of safeguarding.
j) The Safe-Guarding Mat system must provide a means for a readily observable indication that the device is operating.
6. Safety Distance Calculation
The minimum distance calculated is the minimum horizontal distance from the outer edge of the Eurozone Safe-Guarding Mat detection zone to the nearest part of the hazard.
The European prEN-999 formula for floor mounted Safe-Guarding Mats is:
S = (1600 x T) + 1200mm
S is the minimum safety distance is millimeters.
The factor of 1600 is based on the standard assumption of 1600mm/s as the approach speed.
T is the overall stopping time in seconds.
The added 1200mm take into account stride length and arm reach.
The overall stopping time T is made up of two parts: T = t1 + t2
(t1) is the maximum time between actuation of the sensing function and the output signal switching devices being in the OFF state. For the RT6, t1 = 20mS
(t2) is the response time of the machine i.e. the time required to stop the machine of remove the risks after receiving the output from the ME151-4 Safe-Guarding Mat.
The response time of the machine used is the calculations needs to be the worst case time. Some machines have inconsistent response times, which are dependent upon mode of operation, nature of the workpiece and point in the operating cycle at which stopping is initiated. An allowance should be made for wear in brakes etc., if this can affect the response time. An allowance for further delays in the machine control system may be required in some circumstances.
CALCULATION EXAMPLE:
In this example the RT6 is being used with a machine whose worst case response time has been measured as 0.485 seconds.
Using the formula above,
T = t1 +t2
= 20mS + 485mS
= 505mS = 0.505S
S = (1600 x 0.505) + 1200mm
=808 + 1200mm = 2008
Safe-Guarding Mats will be required from 2008mm right up to the edge of the machine baseplate.
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