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4. If your sensor will be used to monitor a process (for example) that will always
go from low RH to high RH, then calibrate it that way. The hysteresis error
will be eliminated.
5. Allow sufficient time for chamber stabilization before calibrating sensors. In
addition, allow sufficient time for the Sensor Under Test to completely
equilibrate before calibrating each point.
6. If you are calibrating an RH transmitter, it will usually have two calibration
adjustments called Offset and Span (or perhaps Zero and Full Scale). It is
usually better to start at the low humidity end and adjust the Offset, and then
go to the high humidity end and adjust the Span. Since the Offset shifts the
entire response curve, it will affect the Span setting and therefore should be
set first.
12.5 RS-232 SERIAL PORT SETUP
The RH CALIBRATOR serial port connector located on the Panel can be used to
operate the unit, program parameters, or output data to a printer, data terminal, or
personal computer. For bi-directional communications (such as with a PC or Terminal),
a communication or terminal emulation software package is needed on the PC. There
are many inexpensive communication programs readily available. Two such programs
are HyperTerminal in Windows XP or earlier, or PROCOMM PLUS by
Quarterdeck/Datastorm Corp.
External Device Connection
Connect an RS-232 cable between the Panel 9-pin female D-Type connector and
the RS-232 serial port of the external device. A 3-wire XON/XOFF cable is all
that is normally required. The serial port is wired as a DTE device (Data Terminal
Equipment); i.e., Transmit (TXD) is pin 2 and Receive (RXD) is pin 3. For
connection to a DCE device (Data Communications Equipment) such as a PC, a
direct pin-to-pin cable can be used. For connection to another DTE device such
as a printer, a null modem adaptor is required.
PC or Terminal Setup
Set the RH-CAL to the preferred baud rate via the Scroll Menu. The available
baud rates are 19.2K, 9600, 4800, 2400, and 1200. For best
performance, the baud rate should be set to the highest rate that the connected
device can accommodate reliably. Set up the PC’s communication program for a
baud rate to match the RH-CAL. The protocol should be 8 data bits, 1 stop bit,
and no parity (N81).
