##### pCO~2~ Equilibrator Users Manual

![](media/image1.wmf){width="4.3902777777777775in"
height="4.045833333333333in"}

**Lamont -- Doherty Earth Observatory**

**CO~2~ Group**

205 Geoscience

####### Rt 9W Palisades, NY 10964

\(914\) 365-8768

**csweeney@ldeo.columbia.edu**

**Table of Contents**

Quick Start [1](#quick-start)

Daily Checks [1](#daily-checks)

Less frequent Adjustments [1](#less-frequent-tasks)

System Description [1](#system-description)

Equilibrator [1](#equilibrator)

CO~2~ analyzer box [2](#pco2-analyzer-box)

CO~2~ Analyzer Box [3](#co2-analyzer-box)

Power up [3](#power-up)

CO~2~ standards and N~2~ gas hook up
[3](#co2-standards-and-n2-gas-hook-up)

Connection of equilibrator sample line and air sample line.
[4](#connection-of-equilibrator-sample-line-and-air-sample-line.)

Ambient Air [4](#ambient-air)

Equilibrated air flow [4](#equilibrated-air-flow)

Setting up uw_pco2.ini file [5](#setting-up-uw_pco2.ini-file)

Software Start up [5](#__RefHeading___Toc496768352)

Maintenance [6](#maintenance)

Flow rates [6](#flow-rates)

Water Manometer [6](#water-manometer)

Pumps [6](#pumps)

Trouble shooting [7](#trouble-shooting)

No sample flow [7](#no-sample-flow)

Error #24 [7](#error-24)

Error #62 [7](#error-62)

No communication between computer and CO~2~ analyzer box.
[7](#no-communication-between-computer-and-co2-analyzer-box.)

Hardware details [7](#hardware-details)

A/D modules [7](#ad-modules)

Solenoids [7](#solenoids)

MetraBytes A/D modules [8](#metrabytes-ad-modules)

#   {#section .unnumbered}

# Quick Start

1.  Plug in CO~2~ analyzer power box.

-   Air pumps should not be on.

2.  Turn IR box "on":

> \- Toggle forward-most switch up.

3.  Check flow for **nitrogen reference gas**:

-   Go to **STEP 2** and turn flowmeter selection output to reference
    gas outlet and set for \~90 ml/min.

4.  Set flows for **standard gases**:

-   Energize solenoid valve while going to **STEP 4** through 10 (even
    \# only).

-   Set flow rates at \~60 ml/min.

5.  Turn on pumps and check flow:

-   Go to **HOME**. Equilibrator and atmospheric air should be flowing
    at 45 ml/min.

6.  Set flow of seawater to equilibrator

-   Bubbles from spray should extend at least 3 inches down from water
    line \~10 L/min.

7.  Check for uw_pco2.ini in C:\\pco2 subdirectory.

-   Make sure that all gas concentrations and serial \# match the
    positions.

8.  Check for C:\\pco2\\data subdirectory in C:\\pco2 subdirectory

9.  Start up program

-   C:\\pco2\>palmeruw

-   Press "F9" to send data to floppy drive (A:).

# Daily Checks

###### Flow rates of gases

-   nitrogen 90 ml/min

-   standards 60 ml/min

-   equil. & atm. 45 ml/min

1.  Water in Manometer

2.  Flow of equilibrator

3.  Check floppy disk space (if using)

4.  Make sure computer time is near GMT

5.  Log any changes to system in GMT

#  Less frequent tasks

1.  Check floppy disk space (every two weeks).

2.  Record offset between temperature readout and calibrated thermometer
    in equilibrator.

3.  Send data to <csweeney@ldeo.columbia.edu> (every two weeks).

# System Description

The pCO~2~ analysis system consists of two major components- a
seawater/air equilibrator and an automated analysis system that uses a
LI-COR infrared analyzer to measure the concentration of CO~2~ gas in
seawater. The partial pressure of CO~2~ is calculated using pressure and
temperature at the time of measurement. The prototype of this system was
operated on the WOCE S4P leg in the Pacific sector of the Southern Ocean
(R/V Akademik Ioffe, Feb.-Apr. 1992) and since May 1992 has been
operating continuously on the R/V Ewing, but has not previously been
described.

## Equilibrator

The equilibrator, shown diagrammatically in figure 1, is based on the
design used by Takahashi during the GEOSECS expedition (Takahashi,
1966). A continuous flow of seawater enters a closed equilibration
chamber through a fine nozzle, producing a fine spray, which enhances
the rate of gas exchange between water and the overlying air. A small
pump continuously re-circulates the headspace air, and a small amount of
the air (nominally 30-50 ml min^-1^) is diverted to the analyzer for
analysis. The air removed for analysis is replaced by means of a
\"controlled leak\" into the equilibrator through a water-manometer,
which allows the rate of replacement to be monitored and which further
assures that the pressure within the equilibrator headspace cannot
differ significantly from the ambient pressure in the laboratory, which
is continuously monitored. The temperature of the water in the
equilibrator is measured with a platinum resistance thermometer, which
is calibrated against a high-precision mercury thermometer traceable to
N.I.S.T. The flow of water into the equilibrator is kept great enough
that the residence time for water is less than five minutes (preferably
less than two minutes, \~ 10 L/min), while the residence time for air is
approximately five hours.

![](media/image2.wmf){width="1.5951388888888889in"
height="2.2666666666666666in"}

**Figure 1.** pCO~2~ equilibrator

A second air pump draws a sample of outside air from an inlet mounted as
high and far forward as possible (to avoid contamination with stack gas)
for analysis as a sample of the ambient atmosphere.

## pCO~2~ analyzer box

Figure 2 shows the components of the analyzer box. Air from the
equilibrator passes through the normally-open ports of two
computer-controlled solenoid valves (plumbed in series) and subsequently
through a countercurrent flow permeation dryer prior to entering the
sample cell of the LI-COR IR analyzer (Model 6251, Lincoln, Nebraska).
The output from the sample cell is directed through a digital flowmeter,
to verify the complete flushing of the cell between analyses. If the
first solenoid valve is energized, the equilibrated air is blocked and
outside air pumped from the forward mast is directed through the dryer
and IR cell. At intervals of no more than every one hour, five
calibration gas mixtures (CO~2~-free nitrogen and CO2 in air) are used
to determine the response of the LI-COR analyzer. The CO~2~-free
nitrogen is also continuously flowed through the reference side of the
IR cell, and the output of the reference side is used to flush the
region of the chopper before being used as the drying gas in the
permeation dryer. In order to insure complete drying of the sample
gases, the **rate of the reference/drying gas flow is kept at least
twice that of the sample gases**. In order to eliminate any possible
excess pressure in the sample cell, the sample gas flows are stopped for
several seconds prior to reading the CO2 signal voltage. The ambient
pressure (which equals the cell pressure with the flow stopped) is
measured using a high-precision electronic barometer (Setra Model 270,
Acton, Massachusetts) each time a sample or calibration gas is analyzed.
IR cell temperature is monitored, but is not required for the
calculation of CO2 concentration.

![](media/image3.wmf){width="2.104861111111111in"
height="2.154861111111111in"}

**Figure 2.** pCO~2~ analyzer box

The output of each of the sensors (IR CO2 signal and cell temperature,
barometric pressure, sample flowrate and equilibrator temperature) is
converted to a digital value using separate A/D converters (modules 1
through 5 respectively) (MetraByte, Models 1131 and 1411, Taunton,
Massachusetts). The modules are daisy-chained into the serial port of a
laptop computer. Digital outputs on two of the A/D modules allow the
computer also to control the operation of the solenoid and
stream-selection valve.

# CO~2~ Analyzer Box

## Power up 

To start up, unplug air pumps until gasses are turned on and drying
incoming air. Meanwhile plug computer and pCO~2~ analyzer box into
appropriate power sources. There are no separate power switches for the
pumps or pCO~2~ analyzer box, although the IR analyzer itself has a
power switch on the lower left side, which must be turned ON (up) AFTER
the pCO~2~ analyzer box has been connected to power. LED position
indicator on Valco valve driver control should be illuminated once power
cable to pCO~2~ analyzer box has been turned on. Digital flow meter
should initially read above 200 (off scale), but reading should drop to
approximately 25 within a few seconds. When IR analyzer is turned on,
the sound of fan should be heard, and within a few minutes a green LED
on the front of the IR analyzer should light up, showing that the
reading is stable. If pressed, each of the momentary solenoid control
switches should cause the appropriate solenoid to operate. Valco valve
position selection switch will drive valve ahead one position (STEP) or
to position 1 (HOME).

## CO~2~ standards and N~2~ gas hook up

Turn on the cylinders of nitrogen (valve position 2) and calibration
gases (positions 4, 6, 8, 10 and possibly 12). The nitrogen connection
has a T connection immediately upon entering the box but no flow
controller. It should be the second connection from the back and the top
row (IR and VALCO 6-position value should be at front of box). The
consecutive positions (i.e. #2, #4, and #6) should be located on the top
row from back to front in increasing order. The consecutive order
continues on the bottom row from front to back (i.e. #8 in front of
#10). We do not have a 5^th^ standard for position #12.

Using the valve position selection switch and the standard gas solenoid
switch, set the **gases to flow at approximately 60 ml/min (90 ml/min
for nitrogen)**, as indicated on the digital flowmeter, by adjusting the
pressure regulators on each cylinder. Hold the gas solenoid switch for
about 10 seconds to get an accurate flow reading.

> **Note**
>
> **Refer to the Reference Sheet inside the cover of the pCO2 Box for
> proper flow settings.**

Once all calibration gas flows are set, turn flowmeter input selection
valve (Figure 2) to the reference gas position (handle horizontal) and
check that the nitrogen reference gas flows at approximately twice that
of the nitrogen (\>100 ml/min). The flow of this gas is set by means of
a crimp restrictor in the line between the Tee and the filter, and can
be reset only by adjusting the crimp. This can be reset by using a
vise-grip pliers and a pair of drill bits to reduce the flow or
vise-grip pliers alone, at right angles to the crimp, to increase the
flow **but should only be done under the direction of Colm Sweeney when
the system is being totally overhauled.** After checking the flow of
reference gas, be sure to **return the flowmeter input selection valve
to the "sample gas" position** (handle vertical).

## Connection of equilibrator sample line and air sample line.

Next, set the flows of equilibrated and ambient air. (When the Standard
gas solenoid is **not** energized, equilibrated air will flow through
the cell, unless the air solenoid is energized to allow ambient air to
flow.) **Maintaining these flows at their proper values is the key to
obtaining accurate analysis and is one of the most difficult aspects of
operating the system**. Since the outputs of the pumps are fixed, and
are much too great to be fed through the analyzer directly, a
complicated system of restrictions (fixed and variable) and shunts or
vents are used to reduce the flows. Aerosol (water and/or salt) and
condensate can collect in the pumps and restrictors, causing changes in
the flowrates, requiring fairly frequent adjustment of the variable
restrictions to balance the flows.

### Ambient Air

The flow of ambient air is likely to have fewer problems. In order to
keep the bow line well flushed with air, the full pumping rate of the
pump is utilized, with most of the flow being subsequently discharged
before reaching the IR analysis system. A Tee with a slightly restricted
vent provides the slight backpressure necessary to give a reasonable
flow through the analyzer. The flow for this is tested by pressing the
atmospheric (labeled "atmos\") solenoid switch. Adjustments to this flow
are made using the needle valve inside the CO~2~ analyzer box (figure
2); gross adjustments require changing the restriction to the vent
downstream from the pump. **Keep the ambient air flow between 35 and 50
ml/min.**

### Equilibrated air flow

Since this air contains fairly large amounts of aerosol, and is
saturated with water vapor at equilibrator temperature, changes in the
flow are more common. In order to keep the residence time of air in the
equilibrator long, excess air cannot be vented, but must be returned to
the equilibrator. Only that portion of the air, which passes through the
analyzer, is discharged. In order to keep the pressures in the vicinity
of the pump close to ambient, simple restrictions to reduce the flow
cannot be used, and a variable shunt between the input and output sides
of the pump is used (Figure 3). The shunt should be opened enough so
that less than \~150 ml/min ofair is being circulated to and from the
equilibrator. Low flow will cut down on moisture and aerosol build up in
the sample lines.

Leaks in the circulation system will be shown by excessive flow of
replacement air into the equilibrator through the water manometer (leak
on high-pressure side of pump) or flow of equilibrated air out through
the manometer (leak on low-pressure side of pump). When the equilibrated
air is flowing through the IR cell, the replacement rate through the
manometer should nearly match that of the flowmeter; when the
equilibrated air is blocked (as during calibration periods) there should
be little or no flow through the manometer. (Excessive rolling of the
ship may cause this comparison to be difficult or impossible to make!)
**As with the ambient air, the flow of equilibrated air through the IR
cell should be kept between 35 and 50 ml/min.** This value is displayed
on the LCD display inside the pCO2 analyzer box as sample flows into the
IR analyzer with brief (\~30 second) interruptions when actual reading
are being taken by the IR analyzer.

![](media/image4.wmf){width="1.8729166666666666in"
height="2.1256944444444446in"}

**Figure 3.** Equilibrator air circulation pump.

**Connect Thermistor and GPS**

The temperature probe (Figure 1) is connected to the CO~2~ analyzer box
by a gray data line. This is connected to a MetraByte A/D module marked
"Thermistor". When the GPS is being used it is connected to the laptop
through the PCMIA slot.

## Setting up uw_pco2.ini file

This file specifies many of the operating parameters for the operating
program of the underway system. Bring DOS screen up and go into pco2
subdirectory by typing:

C:\> **cd pco2 \<Enter\>**

Now type: C:\> **edit uw_pco2.ini \<Enter\>**

The file should look as shown in Figure 4.

32 , 5 , 90 , 70

13.576 , .10732 , 3.110E-5,0,0

3

Nitrogen, 0

ca02231, 236.29

ca02235, 100.00

cc15551, 362.78

ca02205, 495.18

02-18-1999 17:38:22

**Figure 4.** uw_pco2.ini File display use DOS edit

Starting with the first line: It is set for **32** samples between
single runs of **5** standards. Air from the equilibrator will flow for
**90** seconds and the standards will flow for **70** seconds. The
double precision numbers in the second line are the coefficients for the
last calibration that was made and will be updated with each set of
standards. The third line contains the order of the polynomial
(**3**^rd^) used to fit the standards. The fourth through the second
from last lines are the standard IDs and concentrations. The date at the
bottom of the INI file is the last time it was accessed by the
NBP_PCO2.EXE program.

When finished editing press the alt key followed by the down arrow to
select quit. The edit program will prompt you to save changes.

[]{#__RefHeading___Toc496768352 .anchor}

# Software Start up

To start the system operating, turn on the laptop computer, check that
the computer date and time are correct (use GMT), and place a formatted
empty disk in drive A. Drive C should have the pco2 program
(c:\\palmeruw.exe) and the initial file (c:\\uw_pco2.ini). Start the
program by typing:

C:\\pco2\> **palmeruw \<Enter\>**

Within a few seconds the Valco valve should drive to position 2 and the
standard gas solenoid should click (signaling energizing of second
solenoid in series) as the first calibration gas flows. The program is
completely automatic from this point. The following commands will help:

F10 To stop the program. This exit procedure will make certain that the
valves are in the proper shutdown position before ending.

F9 To toggle switch that prints data to floppy. Is **off** when program
starts.

F7 To determine the amount of disk space remaining. **The high-density
floppy disk in drive A: will need to be replaced every two weeks.**

F3 To toggle switch that prints data to ships data acquisition system.
Is **on** when program starts.

The program gives the user the option to save each day\'s data to a
single disk file (F9), assigning a new name each day. There should be
enough room on the disk for roughly two weeks worth of data; to
determine the amount of disk space remaining, the F7 key from within the
program. If less space remains than is required for a single data file
(approximately 70,000 bytes), end the program (F10), replace the data
disk with another high density, formatted disk and restart the program
as above.

# Maintenance

## 

## Flow rates

Once the underway CO~2~ system is started there is very little that
needs to be done except keep an eye on the flow rates of the gases.
Since the equilibrator sample contains large amounts of aerosol, and is
saturated with water vapor at equilibrator temperature, changes in the
flow are more common. In addition to the flowrates, the aerosol trap
(equilibrated air line) and condensate traps (both lines) need to be
checked periodically and emptied as needed.

Flow rates:

Equil. and Atm. Samples: 35-50 ml/ min

Standards: 60 ml/min

Nitrogen 90 ml/min

## Water Manometer

It is best if the water level in the water manometer (Figure 1) is
checked daily to insure that it has not evaporated. The water level on
the equilibrator side of the water manometer should not be higher than
about 1/4 inch above the upper cross tube, or else the pressure in the
equilibrator may be significantly below atmospheric pressure, and the
calculated pCO~2~ will be too low by the same factor. One inch of water
is equivalent to almost 0.3% in pressure, or approximately 1 atm at
values close to atmospheric!

Equilibrator flow

There are relatively few adjustments that can be made on the
equilibrator. A ball valve in the inlet line can be closed partially to
reduce the rate of flow of seawater, or closed completely in the event
of leaking or flooding. The nozzle is attached to a flange, which is
itself attached to the equilibrator top plate by means of four stainless
steel bolts and an O-ring seal. Remove the bolts and carefully withdraw
the entire assembly, taking care not to drop the O-ring into the
equilibrator. The nozzle can probably be cleaned sufficiently by turning
the knurled cone to greatly increase the flow, open the ball valve with
the nozzle loosely in the hole in the equilibrator top to rinse
accumulated particulate matter from the nozzle, and readjust to give
proper spray pattern. If absolutely necessary, the knurled cone can be
removed by twisting in a counter-clockwise direction with vigor.

The water drains from the equilibrator by means of gravity flow from the
overflow in the inner tower; neither the drain line (large-diameter
spiral plastic hose) nor the siphon breaker hole (in the bottom plate of
the equilibrator) should be allowed to become restricted. In the event
the siphon breaker tube becomes restricted, there is the great
likelihood that water will siphon from the equilibrator due to periodic
accumulation/draining of water in the drain line as the ship rolls. This
will cause the pressure of air in the equilibrator to fluctuate greatly,
causing excessive exchange (\"breathing\") between the equilibrator and
the laboratory atmosphere. This will be shown by 2-way air exchange
through the water manometer, in phase with the rolling of the ship. No
meaningful measurements can be obtained until this situation is
rectified (by reducing the restriction on the siphon breaker, re-routing
the drain line to reduce the effect of rolling, or by reducing the flow
rate of incoming water, so that the drain line can keep up with the
input.)

A second drain line, with ball valve, allows the equilibrator to be
completely emptied for servicing or cleaning. In general, this drain
should not be opened except at the end of the cruise, to prepare for
removal of the system.

## Pumps

The KNF Neuberger air pumps have stainless steel heads, but some rust
will form from contact with salt in the aerosol, particularly in the
equilibrated air pump. It pays to occasionally remove the head and clean
the head (using a "Scotch-Brite" pad wetted with water, dried with a
paper wiper). Examine the diaphragm for leaks and the clear plastic
valve plate for cracks at this time. Make sure all the parts are in
their original orientation when reassembling. The four machine screws
which hold it together are rather small diameter, and may "freeze" in
the cast metal base, so a light coating of molybdenum disulfide grease
on the threads should be added at this time as well, taking care not to
get it inside the head.

# Trouble shooting

Trouble shooting the CO~2~ analysis system is like trouble shooting any
other system. Work backwards from the symptom.

## No sample flow

This is a common problem that results from aerosols that will clog up
the equilibrator line. To adjust flow (section 3.1, Figure 3) start by
opening up the pin valve inside the pCO~2~ analyzer subs box. If this is
not creating enough flow then shut down the shunt valve until the flow
rate is high enough. Do not use the back pressure valve to increase flow
because this may not allow circulation of air through the equilibrator.
If non of these procedure give enough flow, then the equilibrator air
line and pin valves should be rinsed through with DI water. Use N~2~ gas
to dry tubing and valves after rinsing.

## Error #24

This is a devise time out error indicating that there was no response
when the data was sent out to the data acquisition system on board. If
this was to a printer it might indicate that there was something wrong
with the printer.

## Error #62

This is a end-of-file error that may show up when you first run the
program. A miss-match between the specified number of standards and
number of standards listed in the uw_pco2.ini file.

## No communication between computer and CO~2~ analyzer box.

In the event of loss of communication with the A/D module stack, check
all connections on the modules and related connections on the terminal
strip for breaks in continuity. Any loss of continuity in the daisy
chain will prevent communication with all of the modules. By wiring the
serial cable directly to any one module (black to GND, red to TRANSMIT
and blue to RECEIVE), the individual module can be addressed using
KERMIT (on the laptop C: drive) (N.B.- UPPERCASE LETTERS MUST BE USED
WHEN COMMUNICATING WITH THE MODULES!). Typing \"#1RS\" from the laptop
should cause the module (1) to respond with its setup configuration, as
given in Table 1. See the MetraByte manual for further information if
the modules need to be reprogrammed. See also the description of the use
of the DEFAULT connection in case the modules will not communicate when
connected directly to the serial cable.

#  Hardware details

## A/D modules

The MetraByte A/D modules are stacked in the lower left portion of the
analyzer enclosure, in numerical order from the bottom of the stack.
Table 1 gives the details of the use and configuration of the modules.

## Solenoids

The solenoid bodies are constructed largely of stainless steel, but some
internal parts will rust when in contact with the salt in the aerosol
from the equilibrator. Once this happens, the oxide will begin to
interact chemically with the CO~2~ of the air passing through. The
effect appears to be chromatographic and reversible. When cool, the
oxide will adsorb carbon dioxide, which it will then release when
heated. Since the "standard" solenoid is held on for approximately six
minutes during the calibration sequence, it will heat up significantly
and will add CO~2~ to the calibration gas passing through. When turned
off at the end of the calibration sequence, the solenoid will cool and
the oxide will again adsorb CO~2~ from the sample gas passing through,
lowering the observed concentration in the first one or several samples.
The solenoids should be examined for corrosion occasionally, and cleaned
(or more realistically, replaced) if a significant amount is found.

modules.

**Table 1** (see MetraByte manual for discussion of modules)

(all modules set for 9600 baud and ECHO ON)

Module \# Signal Configuration (setup) Digital Output 0 Digital Output 1

1 CO2 level 310205C2

2 Cell Temp 320205C2

3 Barometer 330205C2

4 Flowmeter 340205C2

5 Equil Temp 35020DC2

Digital output:

Module \# 0 1

1.Valco valve STEP Valco valve HOME

2.Standard Solenoid Air Solenoid

3.\-\-\-\-\-\-\-\-- \-\-\-\-\-\-\-\--

4.\-\-\-\-\-\-\-\-- \-\-\-\-\-\-\-\--

5.\-\-\-\-\-\-\-\-- \-\-\-\-\-\-\-\--

**Table 2.** Terminal strip connections (top=1 bottom=12)

[connection color pos color connection]{.underline}

A/D module 3 -V gray 1 white Setra barometer

A/D module 3 +V yellow 2 green Setra barometer

jumper to 6 red 3 red Setra barometer

3 red power supply +12V

jumper to 9 black 4 black Setra barometer

4 black power supply -12V

jumper to 10 grn/wht 5 grn/wht power supply 12V

common

5 black flowmeter 0V excitation

jumper to 3 red 6 red flowmeter +12V excitation

A/D module 4 -V green 7 green flowmeter signal gnd

A/D module 4 +V orange 8 white flowmeter signal 0-5VDC

jumper to 4 black 9 black A/D daisy chain gnd

serial cable gnd black 9

jumper to 5 grn/wht 10 red A/D daisy chain +V

serial cable RD red 11 grey A/D module 5 xmit

serial cable SD blue 12 blue A/D module 1 receive

## MetraBytes A/D modules

The modules are "daisychained" together, with the communication output
(transmit) of one connected to the input (receive) of the next in line.
The computer serial port "send data" line is connected to the input of
the first module, and the serial port "receive data" line is connected
to the output of the final module in the chain. This being the case, the
computer can "talk" directly only to the first module, and communication
is only possible with the other modules because each is programmed to
echo anything received on its input to its output (and thus to the next
module in the chain). The result of this echoing is that any command
(mostly requests for readings, or to turn digital outputs on or off)
will be sent through the entire chain and will then appear on the input
of the computer that sent the command in the first place. If the command
is recognized as valid, the addressed module will then send the
requested reading (if that was the command). Anytime the program
requests a reading from a module, the result should be the appearance of
TWO strings at the serial port input- first the echo of the command,
then the reading. Anytime the program requests a change in the state of
one or more of the digital outputs, ONE string will be received by the
computer (the echo only), even though no response is required by the
program. The result is the buffer that holds the characters received by
the serial port will often contain much unneeded information. Therefore,
it is necessary to empty the buffer before requesting a module reading,
and then to "throw away" the first string received after making the
request (the echo of the command). For this reason, the program will be
seen to clear the buffer (by means of an "input" command, with the
string read being ignored) before requesting any reading (the commands
to PRINT to the serial port). After requesting the reading, the program
will take TWO inputs from the serial port, with both being assigned to
the same string (q\$), so that only the second input is actually used.
The number of characters in the input buffer can be checked without
removal by examining the value of the variable "loc(1)" (if the serial
port was opened as #1), but anytime the data in the buffer is read with
an INPUT command, the buffer will be emptied as it is read.