OPTO 22 SNAP PAC R SERIES, Руководство пользователя

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CHAPTER 3: SYSTEM INFORMATION
SNAP PAC R-Series Controller User’s Guide 35
Offset and gain —The controller can calculate offset and gain for analog input points. If a -50 mV to +50 mV
input receives signals that are slightly off (not exactly -50 mV at the lowest point, for example), the offset and
gain can be calculated so that values will appear accurately when read.
NOTE: If you are using Modbus/TCP or EtherNet/IP, you will need to calculate the offset and gain yourself. Then you
can write offset and gain values to the controller.
Output clamping —The controller can clamp values sent to analog output points so they do not go above or
below a specific limit. For example, if you are using a 0–10 VDC output module, but the device attached to
one of its points can handle a maximum of only 5 VDC, you can set an upper clamp of 5 VDC for that point.
The values for upper and lower clamp are set in engineering units.
Average filter weight —The controller can use a filter weight to smooth analog input signals that are erratic
or change suddenly. See details in the PAC Manager User’s Guide .
Additional analog features —The following analog features are available when a SNAP PAC R-series
controller is used with PAC Control. These features are not currently available through PAC Manager or the
memory map. Use PAC Control commands to configure and access them. See the
PAC Control User’s Guide for
more information.
• Ramping —Some devices attached to analog outputs should not be abruptly stepped up or down,
because a sudden change might damage the equipment or cause other problems. Instead, you can
gradually ramp the device up or down to the desired value.
• Analog totalizing —For an analog input, a totalizer accumulates readings by sampling the input point at
set intervals and storing the total value, for example to determine total flow based on a varying flow rate
signal.
Serial Communication
R-series PACs can communicate with serial devices either through the RS-232 connector on top of the
controller (Port 0) or though SNAP serial communication modules on the rack.
The default configuration for Port 0 is communication with a host PC using a modem and PPP. To
communicate with a serial device, first change Port 0’s configuration in PAC Manager. Here are brief
instructions; for more details, see “Configuring Direct Communication to Serial Devices” in the
PAC Manager
User’s Guide (form 1704).
1. In PAC Manager’s Inspect window, click Communications and choose Communication Port Control from
the pop-up menu.
2. For Com Port 0, click PPP in the Control Function field and choose None from the list. Click Apply.
3. Save the configuration to flash memory.
Communication through the RS-232 port is handled through PAC Control commands. See “Communication
Commands” in Chapter 10 of the
PAC Control User’s Guide .
For additional serial connections, use SNAP serial communication modules. Most serial modules provide two
channels of serial data, typically to interface with printers, scales, chart recorders, RFID readers, or Wiegand
®
security devices. A Profibus
®
module provides one channel of data from Profibus DP devices. See the serial
module’s user’s guide for details.
PID Loops
Proportional integral derivative (PID) loops are used to drive a variable, often from an analog input, toward a
desired value. The PID monitors the variable, compares it to the setpoint (the desired value) and calculates an
output that will push the variable very close to the setpoint. Temperature control is a typical application for a
PID.