PC based chart recorder
I have build several PC based chart recorders for perfusion
laboratories
in South Africa. The basic PC based chart recorder has two input
channels. For the older
models each channel only had a pressure input, but the newest models
have a pressure as well as a temperature input, both which can be
displayed and recorded. As an optional extra a third ECG channel may be
added. The software has been optimized to be used with the Langendorff
perfusion system. Below is a picture of an older system with an ECG
channel.
Below are more photos of the connector panels of the new models, one
without an ECG channel and the other one with an ECG channel:
All inputs uses standard DIN connectors, it is therefore not necessary
to buy expensive leads. The ECG unit is a standard 3-lead ECG unit with
a lead select switch and
a variable gain control. The ECG is an electric isolated design, but is
only
intended
for animal use. The pressure input may be used with any resistive
bridge type pressure transducer. The temperature sensor is a NTC
thermistor probe. Below is an example of a pressure transducer and a
photo of the tip of the temperature probe:
Pressure and temperature information are displayed in real-time. To do
calculations on a selection of data is as easy as selecting a region of
the graph display and pressing the 'Calculate' button. Two models are
currently supported, the balloon model and the working heart model.
Below are screenshots of the calculation results for the two models:
Below are some screenshots of the software. The left screenshot shows
the main screen for a two channel setup, while the right screenshot
shows the main screen of a three channel setup:
As can be seen the screen is divided vertically into two or three
windows depending on the number of channels. The
main part of each window consists of the graph. Right next to the graph
are the current real-time statistics. The buttons on the right hand
side are
used to control the specific channel. Each channel also has a dedicated
menu.
Calibrating the chart recorder is also very easy. It is all done
via the calibration window for that channel and input. Below are two
screenshots of the
calibration window, the one on the left is for the pressure input,
while the one on the right is for the temperature input:
A known pressure is put on the transducer, or the the thermistor probe
is kept at a known temperature and the 'Add' button is pressed. The
software then automatically logs the ADC value and asks the user to
enter the actual pressure or temperature value. The necessary
calibration parameters are automatically calculated if there are enough
data points. Calibration points can
be added or deleted at any time, deviations are also shown if there are
enough points, which is an indication of the quality of the calibration
point.
Older models
Below are some photos of older models of chart recorders which I
have build. The first one only consisted of two pressure channels. The
data converter module is a separate unit that is connected via a RS232
serial cable to the PC. This converter module houses the
instrumentation
amplifiers, the analog to digital converters and an 8031
microcontroller
which interfaces the analog to digital converter to the RS232 serial
port
of the PC. Below is a photo of that unit:
Below is a close-up photo of a chart recorder connector panel which has
two pressure inputs and an ECG input:
Below is a close-up photo of a chart recorder connector panel which has
only two pressure inputs:
Below is a photo of the laboratory setup at the perfusion lab of the
University of Stellenbosch:
The PC running the chart recorder software is to the left. The
right-most
column in this photo is currently in use. The two peristaltic pumps are
two Sarns Model 5500 pumps.
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