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.

 Back to laboratory equipment mainpage