44 Section 14: Hardware Interfacing
Many printers, such as those from IBM and HP, have a male connec-
tor, are configured as DCE, and use DTR/DSR handshake. An adapter
for these printer types is shown below.
A computer interface adapter for IBM PCs and compatibles is shown
below. Note that this adapter is supplied as a standard accessory.
This type of adapter is also available as a standard product from
most computer accessory sales companies.
Some computers do not use the standard 25-pin connector. An
adapter is supplied with the HERMIT for connection to an IBM PC/
AT or compatible. The example below shows a connection for the
Epson HX-20.
Finally, many computers do not require an adapter to work. Radio
Shack’s TRS-80 Model 100 is a good example.
Transducers
Transducers other than those provided by In-Situ may be adapted
for use with the HERMIT. Mating connectors must be ordered sepa-
rately from In-Situ. Do not use any other type of connector as this
will compromise the integrity of waterproof operation.
The wiring of a standard 2-
wire 4-20 mA transducer is
shown here. The HERMIT
provides loop power at ap-
proximately 24 VDC and has
a nominal resistance of 185
ohms. Loop power is supplied
only when the instrument needs to take a measurement.
Transducers that require
more power than can be sup-
plied within the 4-20 mA loop
can be used in the 3-wire
configuration shown here.
The source output of the
HERMIT can supply as much
as 100 mA. The output is protected by current-limiting circuitry.
