Ethernet Switch¶
JS-50 ScanHeads are connected with a single cable for both power and data, using the PoE Standard for power delivery and Gigabit Ethernet for data.
A central component of any ScanSystem is the PoE Network Switch. JoeScan does not distribute switches; you must supply your own. On this page, some considerations for choosing a suitable model are listed.
Port Count¶
You will need at least N+2 ports for N ScanHeads. ScanSync modules are PoE powered and need one port, another one is for the uplink to the PC. See below for port speed requirements.
It may be economical to use a switch with more ports than strictly needed. Running at the edge of the power budget is one aspect, others are possible port failures, developer access and future expandability of the ScanSystem.
Power Requirements¶
PoE Standards¶
PoE standards come in three types: IEEE 802.3af, IEEE 802.3at, and IEEE 802.3bt. These standards define the minimum power that Power Sourcing Equipment (PSE) can deliver and the maximum power that Powered Devices (PD) will expect to receive.
| Standard | 802.3af | 802.3at | 802.3bt Type 3 | 802.3bt Type 4 |
|---|---|---|---|---|
| Also known as | PoE | PoE+ | PoE++ | PoE++ |
| Max Device Power | 15.4 Watts | 30 Watts | 60 Watts | 90 Watts |
| JS-50 Compatibility |  |
|
|
 |
| Remarks | Mode A or B only | Four-pair mode not supported |
All JS-50 models use less than 13 Watts of power, and therefore work with the 802.3af standard. There is no need to use network equipment rated for the higher standards, but they will work nonetheless.
Older implementations of Power over Ethernet, commonly named "passive PoE" or similar, will not work for JS-50.
There is no need to measure or adjust PoE voltage if using standards-compliant equipment - the PSE (switch) and PD (ScanHead) will negotiate the needed value.
Power Budget¶
Each PoE switch has a rated PoE budget, i.e. the maximum wattage the switch can supply simultaneously to all connected devices. It is important to select a model that can satisfy the requirements of all connected ScanHeads (and ScanSync) comfortably. Some lower end models can supply standards compliant power to only part of their network port range, even though they may all be labelled with the PoE symbol. A reading of the datasheet should clarify this.
Multiply the number of ScanHeads in your ScanSystem with 15W, if the switch has a power budget rating greater than this number, you are on the safe side.
Cold Start Draw¶
Upon boot-up of the switch, all heads are powered up simultaneously, momentarily maxing out power draw on all ports. Some network switches have shown failures in this case. This is uncommon (and some switches mitigate the effect by staggering the power-up order), but if you experience failures, it may be worth testing if the problems go away when not all heads are connected, i.e. peak load is reduced.
PoE Injectors¶
An alternative to using a PoE Network switch may be to use PoE Injectors, as long as the chosen models are compliant with 802.3af.
Using Poe Injectors is generally not the first choice for production systems, but can be helpful during development to simulate loss of network, and to reset the ScanSync/Encoder in testing.
Nonstandard PoE
Some older UniFi switches also used the PoE branding for what is now termed "passive PoE" and are not compatible with the 802.3af/at standards. These will NOT work with JS-50 ScanHeads.
Managed vs. Unmanaged¶
For production environments, both managed and unmanaged Ethernet switches will work. Managed switches can give some troubleshooting insights if things don't work as expected, but are generally not needed, and from a cost perspective an unmanaged switch is the better choice.
Some managed switches have additional functionality, such as filtering, port mirroring, VLAN tagging or PoE switching. If you need the additional functions, a managed switch can be used.
Managed Switch Gotchas
JoeScan support has seen at least one model of a managed switch (the IGS-6325-24P4X ) that by default filtered the UDP "discovery packets" broadcast by the Pinchot API to find ScanHeads on the network. If you have trouble with ScanHead discovery, it may be worth checking in the Management console of your switch.
Consumer, Business and Industrial variants¶
Most switch manufacturers have different product lines, segmented by application. From a purely functional standpoint, consumer grade switches are sufficient, however, you may want to consider the differences with respect to:
- environmental specs (e.g. operation temperature range, vibration resilience)
- warranty and parts availability
- mounting options (desktop vs rack mount vs DIN rail mount)
- reliability (redundant power supplies)
Port Speeds¶
ScanHead and ScanSync Ports¶
The RJ45 ports for the ScanHeads devices must support 1GBps operation, 100MBps will not be sufficient, even for single-head installs at low data rates. The firmware on the ScanHeads will refuse to connect if a speed below 1Gbps is negotiated. If a head is powered up, but can not be connected to, it may be worth inspecting the speed indicator on the switch. Many switches have a two-color LED per port, showing 
for 100Mbps and 
for 1Gbps. Consult your switch manual for details.
The ScanSync device can be connected to a 100MBps port - it will auto-negotiate this speed even when connected to a 1GBps port, so here the indicator light is fine.
Uplink to PC¶
On larger ScanSystems, consisting of more than 5 units, the uplink port (and the receiving NIC) should support 2.5, 5 or 10 GBps. This is somewhat dependent on scan rate and chosen data format.
Tip
If you suspect that the uplink is a bottleneck, try to set the data format to HALF or QUARTER resolution, this cuts the amount of data transferred accordingly. Under Windows, it is helpful to use the Network Monitor tab of Task Manager to monitor the saturation of the network port.
You can also use an SFP+ module supported by your switch as the uplink to the PC. For longer runs in a noisy mill environment a fiber-optic connection may be a good choice. SFP (without the plus) does not support 10Gbps.
Recommended Models¶
Please contact JoeScan support for a list of recommended models for your scanning application.