With some older €Motion sensors, they are no longer properly recognised via USB. The solution is to download and install drivers from the website, after which the €Motion will be recognised again.
The blood pressure sensor BT17i (or 0377i) is a relatively complicated sensor for which the generation of a relevant graph is difficult to automate. This is because the procedure requires manual selection of relevant datapoints for each measurement. When using this sensor, please take note of the following:
- The procedure for creating a envelope curve is extensively described in the sensors’s User Guide. Read the guide carefully and follow the described steps.
- An example result in which the necessary processing steps have been carried out can be downloaded here. With this example, you know how the data is supposed to look.
- You can also access the instructions in the lesson materials provided here in our library of Teaching Resources.
There are a few tips that make the selection of relevant datapoints easier. In general, more datapoints means that the analysis can be done more accurately. You may, however, already achieve acceptable results using as little as 30 datapoints. Please take note of the following:
- Make sure the measurement takes no longer than 40 to 60 seconds. This can be achieved by tweaking the pressure release valve to allow the cuff to deflate faster.
- First select the interval in which you want to select the datapoints. This can be done by choosing “Range” instead of “Point-to-point” in the “Select/Remove Data” window. This considerably reduces the amount of points, making it easier to select relevant datapoints.
- Maximize the selection screen by setting the window to full size using the icon in the top right corner of the window. The selection of points is easier when using a large window.
If you succeeded in selecting relevant datapoints and performing other processing steps, but did not get a envelope curve, please take note of the following:
- It is possible that the range for p_trend was too small. The best results are acquired with a 40 – 140 mmHg range. When a smaller interval is used, part of the curve may be lost. Select datapoints over the entire interval. Especially the datapoints at 40 and 140 mmHg are important for the envelope curve.
- The smoothing for p_pulse or p_trend may be wrong. In this case, the envelope curve is plotted over the entire range, but the actual envelope shape is not visible. This may be caused by insufficient/incomplete datapoint in one of the two measurements (either p_pulse or p_trend), for example when the selected points are in a smaller range or not distributed over the entire range. It is good practice to always select the accompanying local minimum (p_trend) for every local maximum (p_pulse).
If a force is exerted on the sensor larger than the maximally allowed force (> 80 N), the internal mechanism will lose its elasticity. The sensor will no longer function properly afterwards and will have to be replaced.
Yes, this is normal behavior. The sensor uses a Hall-element which always gives a sinusoidal signal with an amplitude of approximately 2,5 mT on top of the measured signal. This is called “1/f noise”.
This may be caused by several factors:
- The test subject is moving during the measurement. Let the test subject sit in a chair relaxed, with their arm lying at their side or on a table when data are being collected.
- The used sampling frequency may influence the amount of detected noise. A sampling frequency of 50 Hz is high enough to measure an ECG signal but there will be not much noise detected. A sampling frequency of 200 Hz detects a lot more noise.
- The sensor can also be used to measure electrical signals of contracted muscles. To obtain a nice ECG signal, it is necessary that the muscles of the arms (and also other muscles) are as relaxed as possible.
- For the older CMA ECG set, the electrodes are connected to the amplifier via 4 mm wires. Two parallel wires act as an antenna and catch noise from the power grid. Wrap the wires around each other a few times to get rid of this noise.
A possible cause for this phenomenon is a measurement frequency that is too high. The sampling frequency used in experiments with a motion detector is limited by the speed of sound in air (about 340 m/s): if a distance of 10 m is measured, the sound pulse takes about 59 ms to travel from the motion detector to an object and back. This means that if a sample frequency of more than 17 Hz is used, a new sound pulse is emitted before the previous one is received, leading to erratic readings. The maximal frequency is also limited by the conditions of the experiment. Typical sampling frequencies are: 1 m range – 40 Hz. 2 m to 6 m range – 25 Hz and 6 m to 10 m range – 10 Hz.
The sensor makes use of an electrochemical cell to determine the oxygen concentration. This cell will deteriorate over time, which limits the shelf-life of the sensor to 2 or 3 years. The sensor needs to be replaced after this period.
Yes, CMA supplies a CO2 to O2 Tee coupling piece (art. No. 07661) which fits the sampling bottle to which the two gas sensors can be connected.
When the sensor is collecting data, the intensity of its IR source is modulated (the sensor takes a reading about every 3 s). If the sampling frequency is set to a higher value, the CO2 readings will have some fluctuations (between readings taken when the IR source is on and the readings taken when the IR source is off).
The CO2 sensor can be calibrated using the calibration button on the sensor box. This button sets the reading of the sensor to a value around 400 ppm CO2 (the theoretical CO2 concentration value in fresh air).
- Place the 250 mL sampling bottle delivered with your sensor in the air outside long enough to ensure that its content is replaced with fresh air.
- While still outdoors, insert the sensor with the rubber stopper into the bottle. You can now take the bottle and the sensor to the location where the measurements will be performed.
- Connect the CO2 sensor to an interface and let the sensor warm up by collecting data for at least 5 minutes.
- When the readings stabilize use a paper clip or a ballpoint to press down the calibration button. After about 30 seconds, the reading should stabilize at a value around 400 ppm.
From a teacher we got a tip for checking the accuracy of the spirometer. The calibration can be controlled with two drain tubes of known content, pressed into each other and closed off. One tube section is filled with water, the other remains empty. Connect the spirometer to the empty tube at the closed side (spirometer 0378i or BT82i). Start a measurement and slide the empty tube into the water-filled tube section. The trapped air escapes through the spirometer. Because the volume of this air is known, the calibration of the spirometer can be established. Make sure that no water gets into the spirometer.
A spirometer measures the rate of air flow in liters per second. The total volume of air that has moved through the spirometer can be calculated by integrating the air flow rate as a function of time. Use the function Analyze/Process > Integral for this.
When the air flow data is converted to volume you may find an upward or downward trend in the volume data. You may apply a drift correction to the collected data in one of the following ways:
- before you start your measurement set the signal measured by the sensor to zero by right clicking the sensor icon on the screen panel and choosing ‘Set to zero’, or
- correct the data after the measurement is finished: determine a straight line through the drift by using the Function fit option and then use a formula to subtract the drift data from the measured sensor data