I beleive that some of the DCC systems have had smph on their remotes several years ahead of the development/release of DCS.
Chuck
ProtoSound 2 locomotives have been out for 12 years now and DCS sets with handhelds and remotes came out 10 years ago. Back then most DCC systems only had 28 speed steps total so you couldn't do SMPH and have a normal speed range. Some DCC guys still run that way and one HO oriented magazine still uses 28 throttle steps in their product evaluations.
You may be thinking of a locomotive that BLI advertised some years ago as coming with factory DCC and and speed control in SMPH. They didn't have a speed measurement technology to do it accurately but they did advertise it. BLI quit advertising the feature after receiving a letter on the subject from MTH since they had already claimed SMPH as a unique feature in the DCS patent.
Does anybody know of MTHs smph is even accurate?
Flash
Yes, MTH locomotives accurately measure SMPH. And MTH locomotives are very consistent. They will match each other within a fraction of an SMPH and they will do it hot or cold, old or new, steam, diesel or electric.
I have spent hours speed maping DCC locomotives so they will match other locomotives in a consist. The speed measurement used in most DCC decoders is BEMF. Unfortunately BEMF is only a relative measurement and changes with motor temperature. Proto2 and Proto3 use an optical tachometer for absolute speed measurement that does not change with motor temp.
The best way I have found to speed map a DCC locomotive is to use a Proto3 locomotive as your speed standard.
I assume the tach reader figures the rpm of the motor and then computes the speed using the gear ratio of the truck and sends this back to the remote.
Ron
You assumption is a little off. While DCS can use its two way communication capability to send an acknowledgement back to the TIU that a speed command has been received all the computation takes place within the locomotive. The remote sends a speed command, the TIU relays the command to the locomotive and the locomotive compares the actual motor speed to the commanded values and adjusts the power sent to the motor until the values match. The number you see on your remote is the speed you are commanding. If the locomotive does not receive the command the locomotive speed will not match what you see on the remote although you may get an error message.
One feature of Proto2 and Proto3 that many people are not aware of is that the track voltage is used for the speed command when running in conventional mode. The locomotives internal electronics use the tachometer to measure speed in SMPH and compares the measured value to the speed "commanded" by steady track voltage. The locomotives internal computer then adjusts the duration of the full voltage DC pulse (track voltage or 12 volts, whichever is lower) to the motor until the actual and commanded speeds match. That is why cruise control works in conventional mode.
Model train magazines usually report starting voltage or speed at a certain voltage in product reviews. It seems that some train magazines aren't too well equipped to measure voltage, speed or both. I read one review of a Proto3 locomotive where the starting speed was listed as three different values in three different places in one review! The model press needs testing equipment and procedures accurate enough to measure performance that are at least as accurate as the locomotives they are trying to measure. Proto2 and Proto3 locomotives are very accurate and very consistent.
