Limit Monitoring and Local Real-Time Control
Measured data is continuously evaluated with respect to three user-defined limit zones (HI, OK, and LOW). Real-time limit status is indicated by front-panel LCD annunciators, while a corresponding TTL/CMOS-level control output is issued from the rear Logic I/O Connector.
Each logic output is isolated to ± 1500 V and provides up to 50 mA for driving external devices directly. You can set the HIGH LIMIT and LOW LIMIT outputs to be either latching or nonlatching, as required by your application. For any nonlatching limit, you can define a hysteresis window to prevent toggling of the limit from signal noise.
A user-scalable ±5 VDC ANALOG OUTPUT is generated for connection to a strip-chart recorder or other device. This analog output can also be used as feedback for a PID control loop.
Peak Capture and Track/Hold Operation
The Model 3540 Frequency Input Conditioner employs a digital technique for capturing the most positive measurement reading since the instrument was last reset. For all other 3500 Series models, peak capture is a purely analog function, the last-captured positive maximum being digitally held until a higher input-signal value is perceived or the instrument is reset.
Any 3500 instrument can be placed in TRACK/HOLD mode (instead of peak capture). When this is the case, the instrument can be commanded to freeze the present value of the analog input signal, without decay, until a command is received to return to normal "TRACK" operation.
Both peak capture and track/hold modes may be controlled by front-panel buttons, by a rear-panel logic input, or by mnemonic commands received at the instrument's RS232/RS485 Interface Port.
Front-Panel or Remote Setup
All 3500 instruments can be completely set up and operated either through the front-panel keypad or through simple English mnemonic commands received from an external computer or terminal through the RS232/RS485 Interface Port.
Entry of a unique configuration security code, if desired, prevents an operator from modifying the existing setup via the fron panel. All setup values are automatically stored in nonvolatile memory, for complete poweroff protection.
In addition to its network setup and configuration "cloning" functions, Daytronic's StartPAC 100 software includes a simple terminal emulation program that lets you issue any standard 3500 Series commands from a remote PC.
Single- or Multinode Data Communications
Each 3500 instrument's 9-pin RS232/RS485 Interface Port permits data interchanges of up to 153.6K baud. Current measurement data is transmitted from this port in response to an interrogation from an external computer or terminal, or in response to a PRINT command from a front-panel push button or logic-level input.
The user can format data transmissions by specifying a terminating character string, optional header and tailer strings, optional node-number "echo," and optional limit-status indication.
The Interface Port can be easily configured for either single-node, full-handshake RS232 communications or multinode RS485 communications.
Single-Node (RS232) Communications
In single-node operation, the 3500 instrument connects to a supervisory computer that can control the unit directly via simple ASCII mnemonic commands—or to a printer, recorder, "dumb" terminal, or other RS232 device.
When the instrument is set for RS232 communications, you can specify the time interval that is to occur between successive automatic hard-copy transmissions (up to 68 minutes).
Single-node RS422 communications are made possible by an optional interface adaptor Model 10E422.
Multinode (RS485 Network) Communications
In multinode operation, the 3500 instrument can be a member of a high-speed multidrop network of up to 99 3500 Series data-collection instruments, mixed as desired.
Network interchanges take place over simple twisted-pair RS485 "daisy-chain" linkage, at standard baud rates from 300 through 153.6K.
In a multinode network like the one shown above, the host computer can "open" any selected node by issuing an OPEN (OPN) command to the entire network. Only one node can be "open" at any one time. The currently "open" node (only) will respond to all subsequent commands issued to the network—including all requests for "local" measured and/or calculated data.
Simple polling routines let your computer optimize network transfer speed as it interrogates a sequence of nodes and receives appropriate response inputs.
For easy configuration and monitoring of a multinode network, Daytronic's StartPAC 100 software is available free of charge.