A fifteen-year-old analyzer sits in the instrument room, and the only data path out of it is the DB9 on the back panel, wired to the workstation beside it. The second computer in the office next door wants the same spectra, and the only options are walking over or carrying the instrument across. The instrument room is on the fourth floor, the office on the second; neither is convenient.
What blocks this requirement is not networking capability. Four things on the instrument side cannot be touched: the case cannot be opened, the data cannot be altered, there is only one port, and the position keeps changing. Match those four one by one and only the model selection is left.
The standard approach in a lab is to put a serial to ethernet converter beside the instrument: serial on one side, a network cable on the other, and nothing installed inside the instrument.
An analyzer that has been through installation and operational qualification usually needs the qualification redone once a board goes inside the case or a driver goes on the instrument. Most instruments add a second restriction: the serial port is the only interface opened to the outside, and acquisition and reporting run through the vendor's own software, leaving no room for third-party programs.
That leaves the box outside the case. The converter moves bytes: it packs serial data into TCP packets and unpacks them back into serial frames in the other direction, without parsing the content. The instrument still sees a serial cable and no network on the far side. Copy the four serial parameters and the flow control setting from the instrument manual first; not every older analyzer is 8-N-1 on data bits and parity, and getting one wrong shows up as a connection that opens and stays silent. When in doubt, read the instrument once through a USB to serial cable at the bench, note the parameters that work, and enter them in the converter.
One step is easy to get wrong: the box arrives with a long feature list, so Modbus to TCP, JSON reporting and edge computing all get switched on during testing. An instrument that has already been qualified is better left on plain transparent transmission, with protocol conversion and data processing off, so the instrument log and original records read as they did before, and nobody has to wonder later which end changed a number.
A serial port is point to point: one line, two directions. When several workstations need the same instrument, separate two roles: who sends commands, and who only listens.
Reading can be shared. In TCP Server mode the converter sends the serial data to every client that is connected, so several workstations receive the same live stream. Writing has to stay on one path: analyzers are mostly question-and-answer devices, and two command streams collide, returning a reply that neither side recognizes. The collision has a signature: a command goes out and the reply belongs to the previous one, after which the records on both ends are out of step.
Older acquisition software only knows COM ports, which is what the virtual COM utility is for: install it once on each Windows workstation, map the same IP address and port to a local COM port, and the software opens it as before with no code changed. One lab integrator has mentioned a hospital clinical lab where analyzers have been connected to workstations this way for twenty years.
RS232 is a single-ended signal: one cable, two devices, and the run gives out after about fifteen meters, which rules out a pull between floors. The Ethernet side uses the building's existing LAN, with the converter on the instrument side and one cable to the floor switch. Keep the serial run between box and instrument as short as possible and hand the rest to the network cable; that is the normal arrangement once the fifteen-meter limit is in play.
Power and placement need settling early: a lab bench rarely has a 24 V terminal, and often no DIN rail behind the instrument. A box-type model such as the USR-TCP232-410s takes either a DC jack or a terminal block, uses a metal case for cooling, runs on a wide input range with reverse polarity protection, mounts on a wall, and covers -40 to 85 degrees Celsius, so it fits under the bench or behind the instrument.
Instruments moving rooms is the most common follow-on action here. The box travels with the instrument, the network cable is re-run, and the IP address moves to the new subnet; the port number and software configuration on the workstation side stay untouched, because the mapping hangs on the IP address and port, not on a physical location.
The reverse lesson comes from the USB to serial route: a new computer needs the driver reinstalled, port numbers drift, the hard-coded COM3 in the software finds nothing, and someone has to make the trip. Export the configuration before the move, put the room number and date in the file name, and import it after the subnet change; steadier than retyping the old screens.
One more detail: the converter needs a fixed IP address, either static or reserved in DHCP. Otherwise the address changes after a power cycle, the saved session cannot connect, and the symptom looks like a dead instrument.
Configured one at a time, IP addresses, parameter sheets, cables, power and acceptance checks grow with the instrument count, and every unit gets its parameters checked separately. With two instruments side by side, a two-port unit saves that work. The USR-N520 carries two serial ports (RS232/485/422 on the H7 version, two RS232/485 ports on the H7-6 version) in a 150 x 98.8 x 30 mm case, takes DC 5-36 V with reverse polarity protection, and supports SSL/TLS with two-way certificate authentication, a Modbus gateway, EMC protection and a built-in watchdog, at one IP address and on one parameter sheet.
A manufacturer building the instrument has another route: put the converter inside the machine. The USR-DR132 for RS232 and the USR-DR134 for RS485 are single-port units the size of a lipstick, with push-in terminals that need no screwdriver, -40 to 85 degrees Celsius, hardware and software watchdogs and automatic reconnection, small enough for a narrow gap inside the enclosure. An instrument that ships with Ethernet built in leaves the customer nothing to solve at the site.
Only two questions remain: how many ports the instrument side needs, and where the box goes. Most requirements of this kind start with "just one port", so one single-port unit will do, without buying ahead for an expansion with no date. The value of a lab instrument is that it measures well and lasts; what a serial to ethernet converter has to do is let more workstations use that value, not make decisions for the instrument.
It packs and unpacks only, with no parsing of the content, so in transparent mode the bytes go in and come out unchanged. The risk is not the converter itself but the features switched on around it: leave protocol conversion and JSON reporting off, and an instrument that has been qualified keeps its original records identical to the pre-upgrade set.
Reading yes: in TCP Server mode the serial data goes to every connected client. Writing should stay on one path, since analyzers work in question-and-answer mode and two command streams interrupt each other. The workable arrangement is to fix one workstation as the command channel and leave the others read-only.
That depends on what the acquisition software accepts. Software that only opens COM ports needs the virtual COM utility once, mapping the network port to a local port number; software that can open a TCP connection needs nothing installed, just the IP address and port.
Check the manual and the connector: RS232 is usually a DB9, single-ended, two devices per cable, about fifteen meters; RS485 is a differential bus that takes several devices over several hundred meters and needs termination resistors at the far end. The two use different electrical levels, so a passive adapter cable will not connect them.
The converter exposes an Ethernet port, so the wireless hop belongs to the on-site access point or a wireless bridge; where needed, the network cable goes to the access point. With a model that has its own radio, confirm it can join an existing network as a client rather than only broadcasting its own hotspot.
The serial side is the short leg: about fifteen meters on RS232 and several hundred on RS485. Ethernet allows 100 meters per cable run, beyond which a switch or fiber is needed. Between floors the building LAN carries the traffic, and the serial limit no longer applies.
The box goes with the instrument, the network cable is re-run, and the IP address moves to the new subnet. On the workstation side the mapping hangs on the IP address and port, so the port number and software configuration normally stay as they are. A static address or a DHCP reservation avoids surprises after a restart.
Yes, without mapping the serial port to the public internet. Send the converter through a VPN or the lab's existing remote access channel into the internal network, then connect to th
