KVM Extender Selection Criteria
Industrial keyboards, video monitors, and/or mice are usually located within 6 feet or 2 meters of the source PC or thin client. However, there are times when you need to mount an industrial display farther away from the source signal—sometimes in a different building or type of location, such as outdoors, on the process floor, and/or in a hazardous location.
One solution is a keyboard video mouse (KVM) extender, which is essentially an extension cord for the KVM signals. In this blog, we will discuss selection criteria and applications for KVM extenders. The KVM consists of 2 primary components—a transceiver from the PC (local KVM) and a receiver at the remote display (remote KVM). The KVM converts and compresses the industrial keyboard, video, and mouse signals into a proprietary data stream transmitted over Cat5 cables or fiber optic cables. Fiber optic solutions can be single mode for long distances (i.e., miles/KM) or multimode for noise immunity. To extend the fiber optic signal, the proper wavelengths must be used for the retransmission of the signals. If there is no match, the signal is lost, and there is no communication between the PC and the remote monitor.
For Cat5 applications, it is important to remember that while Cat5 cable is used for Ethernet communication, KVM extenders do not communicate via Ethernet packets, but rather through proprietary protocols. In all cases, the local and remote KVMs must come from the same vendor. If they do not match, communication with the remote monitor will not take place.
Application: Remote Monitoring or Control Transfer versus Mirroring or Cloning the Monitor
Some applications mount a PC in the control room with the PLC or DCS, while the display is mounted on the plant floor or in some remote control room. This is normally called remote monitoring, although some refer to it as “transfer of control.”
Another variation is cloning or mirroring the control room display with one or more remote monitors. In this case, the operator can be in the control room or at one of the remote monitor sites. The last one to touch the keyboard, pointing device, or touchscreen has control. This is used in applications such as tank farms and chemical column control, as well as a number of oil & gas applications, from upstream logging while drilling to downstream tank farm control and custody transfer.
Criteria for selecting a KVM extender in order of priority:
- Distance vs. resolution
- Mirror/clone vs. control transfer/remote monitor
- Peripheral support
- Media and tuning
Distance vs. Resolution
There is an inverse relationship between distance and resolution. Typically, KVM display resolution decreases with increasing distance, and distance is measured in actual routing versus “as the crow flies.” The bottom line: determine the resolution of the display you are planning to use and be sure the KVM pair can drive that display resolution for your target distance.
Mirror/ Clone vs. Control Transfer/ Remote Monitor
Determine if the remote display will mirror the control room monitor if the remote display is connected directly to the PC in the control room. If it is mirroring the control room display, the transceiver KVM must have local peripheral support, including video, keyboard, and/or mouse. This mirroring capability increases the cost of the local transceiver. Also, pay attention to the peripheral outputs from the PC and the local and remote peripheral ports. Installing signal converters lowers system reliability and troubleshooting complexity is increased by orders of magnitude.
Determine if the remote display will monitor only or have some control capability. If control is desired, determine the components (keyboard, mouse/pointing device, and/or touchscreen) and the communication interface—usually VGA/DVI, PS2/USB and most importantly, the touchscreen will be RS-232—NOT USB. The USB port is incompatible with single-point touchscreens AND multitouch touchscreens due to the encoding methodology used by KVM designers. KVM manufacturers will include audio ports with the serial port.
For video, determine whether the interface will be DVI or VGA. In industrial applications, it is rare to find a KVM extender with HDMI or DP interfaces. One additional point—if mirroring or cloning the display, both the local and remote displays must use the same resolution. So if a 19” 5:4 1280x1024 display is used, the remote display will use the same 1280x1024 resolution. Mixing widescreen HD and lower resolution displays leads to either no image or reduced-sized images.
Here the choice is partially dictated by distance and environment. For instance, both copper and multimode fiber can transmit the same distance. However, fiber provides noise immunity, although for a significant cost penalty.
Tuning vs. Synchronization
Some lower-priced KVM pairs require tuning to perfect the image, and this tuning may be required seasonally based on significant temperature shifts. This is essential when transmitting over long distances. Some higher-end KVMs have auto-synchronization that optimize the image, while others have DIP switches for fixing the receiver/transceiver pair for specific resolution. This difference may be critical when using a high-resolution widescreen display at a considerable distance.
In the table below, we’ve highlighted the key parameters based on our KVM extenders.
These KVM extenders are optimized for max resolution at maximum distances, and contain ports for all the necessary peripherals including touchscreen interfaces. Moreover, they are evaluated and UL listed for Class II, Division 2 installation. They include hardware to lock down the peripheral interfaces as required for Division 2 installation and wiring methods.
These are the only UL listed Class I Division 2 rated KVM extenders. They are part of our portfolio of industrial-grade HMI components, and part of our industrial-grade workstations for remote monitoring applications. Installation may be in Division 2, or with proper equipment, in Division 1 environments.
Selecting the correct KVM extenders is a matter of choosing the right options and understanding the trade-offs and how you plan to implement your remote monitor. If you select correctly, it’s like plugging in an extension cord. If not, the remote monitor will be left in darkness.