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Incorrect RPM reading io540 RV10
- Thread starter Charlrv9
- Start date
- Joined
- Mar 23, 2005
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You might have to experiment a little. Here are the instructions from page 7-39 of the SkyView System Installation Manual (Revision Y, dated April 2016.)
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Tachometer Transducer
If you have a dedicated tachometer transducer (usually with a 12 volt output), you may simply connect its output to the Standard RPM Left input on the SV-EMS-220/221. Ensure that you follow all recommendations given in the manual for your individual tachometer transducer. P-lead pickoff (Lycoming and Continental) If you do not have a dedicated tachometer pickoff, you must follow the instructions below.
Use the two included 30 k[ch8486] resistors (color bands: orange, black, brown, red, brown; connect in either direction) to attach left and right P-leads to the standard RPM Left and RPM Right inputs on the SV-EMS-220/221. Connect them as shown in Figure 50. It is important to connect each resistor as close as possible to the spot where you tap into the P-lead. This minimizes the length of cable carrying high voltage spikes.
Six-cylinder Lycoming engines sometimes need more inline resistance to prevent false readings by the SV-EMS-220/221. If you supply your own resistors, they need not be exactly 30 k[ch8486]. Additionally, both 1/4W and 1/2W resistors are cceptable to use.
Figure 50 – Magneto Pick Off
If, after setting the PULS/REV R and L values as described in the Engine Information Section, you see unstable RPM, you may need to increase the series resistance. We recommend increasing the resistance in increments of approximately 30 k[ch8486] – approx. 30 k[ch8486], approx. 60 k[ch8486], approx. 90 k[ch8486], approx. 120 k[ch8486], and approx. 150 k[ch8486]. Try each value in sequence. A higher resistance value is not necessarily “better”, as too high a resistance can reduce the amplitude of the RPM signal to the point where you may see no, or low, RPM.
===============
Tachometer Transducer
If you have a dedicated tachometer transducer (usually with a 12 volt output), you may simply connect its output to the Standard RPM Left input on the SV-EMS-220/221. Ensure that you follow all recommendations given in the manual for your individual tachometer transducer. P-lead pickoff (Lycoming and Continental) If you do not have a dedicated tachometer pickoff, you must follow the instructions below.
Use the two included 30 k[ch8486] resistors (color bands: orange, black, brown, red, brown; connect in either direction) to attach left and right P-leads to the standard RPM Left and RPM Right inputs on the SV-EMS-220/221. Connect them as shown in Figure 50. It is important to connect each resistor as close as possible to the spot where you tap into the P-lead. This minimizes the length of cable carrying high voltage spikes.
Six-cylinder Lycoming engines sometimes need more inline resistance to prevent false readings by the SV-EMS-220/221. If you supply your own resistors, they need not be exactly 30 k[ch8486]. Additionally, both 1/4W and 1/2W resistors are cceptable to use.
Figure 50 – Magneto Pick Off
If, after setting the PULS/REV R and L values as described in the Engine Information Section, you see unstable RPM, you may need to increase the series resistance. We recommend increasing the resistance in increments of approximately 30 k[ch8486] – approx. 30 k[ch8486], approx. 60 k[ch8486], approx. 90 k[ch8486], approx. 120 k[ch8486], and approx. 150 k[ch8486]. Try each value in sequence. A higher resistance value is not necessarily “better”, as too high a resistance can reduce the amplitude of the RPM signal to the point where you may see no, or low, RPM.
- Joined
- Mar 23, 2005
- Messages
- 13,226
1.5 should be correct for a six-cylinder engine.
The resistor you are adding is to voltage-divide the lead voltage, since the SkyView input only needs 10 volts. SkyView only reads the positive side of the voltage pulse, and sometimes if there is ringing the negative pulse may go slightly positive and give a false extra signal. The resistor is therefore damping that signal, so the ringing never goes positive.
(In some cases, if you find that your RPM seems off by half, you might try setting the pulse ratio to 3.)
The resistor you are adding is to voltage-divide the lead voltage, since the SkyView input only needs 10 volts. SkyView only reads the positive side of the voltage pulse, and sometimes if there is ringing the negative pulse may go slightly positive and give a false extra signal. The resistor is therefore damping that signal, so the ringing never goes positive.
(In some cases, if you find that your RPM seems off by half, you might try setting the pulse ratio to 3.)