General Cautions for Solid State Devices

General Cautions and Recommendations from FWMurphy for solid state devices such as the following models:

Pressure Devices (MDM45, PXMS), Temperature Devices (MDTM, TDX6, RTDT(X)), Speed Measuring And Controlling (HD9063, OS77, SS300, ATA, ATS, ATHA, MT90, SD35HL, MTH6, SHD30, SHD45, HD35), Engine Panels (ST SERIES, EA150), Automation Systems (S400,S500,S510), Engine Controls (EMS447, EMS448, EMS547, MEMIS, GPM92, A91, ASM150, ASM160, A900), Compressor Panel Components (LCDT, MARK III, MARK IV, TTDJ, S1501), Gen-set Controls (MGC, AS SERIES), Murphylink Components (MDDM, MURPHYLINK GAGES), and Communications Solutions (RL2000,RL4000).

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.

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.

Welding Precautions
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 components.

  1. Open the control panel and any associated sub-panels or swing panels.
  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.