And Recommendations from FWMurphy
For SOLID STATE DEVICES such as the following models:
EMS447, EMS448, EMS547, MEMIS, GPM92, A91,
ASM150, ASM160, A900
MDTM, TDX6, RTDT(X)
SPEED MEASURING AND CONTROLLING
HD9063, OS77, SS300, ATA, ATS, ATHA, MT90,
SD35HL, MTH6, SHD30, SHD45, HD35
ST SERIES, EA150
COMPRESSOR PANEL COMPONENTS
LCDT, MARK III, MARK IV, TTDJ, S1501
MGC, AS SERIES
MDDM, MURPHYLINK GAGES
Connect to battery for your direct DC power.
FWMurphy recommends that the power source (+ and -) connection points of any panel containing any solid state device, such as
those listed above, be made directly to the terminals of the battery
(+ and -). This will allow the battery to act as a filter and absorb any
voltage spikes or noise generated by the alternator or other devices
located on the equipment being controlled by the solid-state device.
The preferred method is to tie the negative battery terminal to proper earth ground, (i.e. earth ground rod) and tie any needed
frame/chassis grounds to that same point as well. Connection of
power and DC common at any other point will cause increased noise
susceptibility in the system. Depending on the actual configuration
of the end application, this can cause various control problems,
such as erratic operation, inaccurate sender/transducer readings,
remote communication problems, etc.
FWMurphy recommends that no welding take place directly on the
equipment or on the equipment that is physically connected to
equipment where solid state electronics are used. If welding must
be performed on this equipment, FWMurphy recommends that the
following precautions are taken to reduce the chance of the solid
state electronics being permanently damaged, or damaged enough
to fail at some later time. FWMurphy will not warrant any device
that has been subjected to damage caused by welding.
These precautions will lessen the chance that a high electrical
potential will pass through or across the control panel and/or its
Use reverse biased diode with inductive loads.
FWMurphy recommends that any inductive load tied to a solid-state
output (relays, solenoids, valves, actuators, rack pullers, etc.) have a
reverse biased diode across the coil to snub the inductive kickback.
This prevents the field collapse of the coil from damaging the solidstate output devices and keeps the DC power "clean" from spikes.
1. Open the control panel and any associated sub-panels or
2. Disconnect power and ground connections; and all ribbon and
other cable types leading to or from any solid state device (i.e.
those listed above). Note: Most cables should have a keyed connector for ease of reconnecting, or have removable terminal
blocks. Even if this is an outdoor field repair, wires should be
removed from screw terminals where necessary to prevent any
possibility of damage.
3. Attach the welders’ ground clamp as close as possible to the
area where the welding will occur and use the lowest feasible
setting of the welding machine output.
FWMurphy P.O. Box 470248, Tulsa, Oklahoma 74147 USA (918) 317-4100 fax (918) 317-4266 e-mail [email protected] www.fwmurphy.com