SD/SA/SR640 Dual Speed Ratio Meters RPM, Speed ratio, Reciprocal speed, sum/differential speed-(2)encoders

Model Numbers

SD 640-644  Speed and Rate Meter (RS232 interface) 
SA 640-644 Speed and Rate Meter (RS232 interface, analogue output) 
SR 640-644  Speed and Rate Meter (RS232 and RS485 interface) 


  • The frequency meters shown here provide exactly the same technical properties and fucntions as series SD/SA/SR 340 shown above
  • Moreover, these models are addictionally equipped with 4 output relays (one dry changeover contact each)
  • Accodering to need, these models are also available with up to four front thumbwheel switch sets (preselection switches)
  • Front Dimenions 96 x 96mm (3.78 x 3.78")
  • All available models and possible cominations are clearly described in the PDF operating instructions


SD340 Speed Ratio Meter Diagram


AC Power Supply 24 V~ ±10%, 15 VA 
 DC Power Supply

24V  - (17 - 40V), approx. 100 mA (+encoder)

 Aux. encoder supply outputs

2 x 5,2 VDC, 150mA each

2 x 24 VDC, 120mA each 


2 universal encoder inputs (Ri = 8.5kΩ each channel)

4 digital control inputs HTL (Ri = 3.3 kΩ)  

Low < 2.5 V, High > 10V, min. Pulse width 50 µsec.

 Max frequency (per encoder)

RS422 and TTL differential: 1 MHz

HTL single ended: 200 kHz 

TTL single ended: 200 kHz

Switching outputs (all models) 

4 fast power transistors 5 - 30V, 350 mA (b)

Response time < 1 msec. (a) 

 Serial link

SD / SA: RS232, 2400-38400 Bauds

SR: RS232 and RS485, 2400 - 38400 Bauds 

 Analogue outputs (Models SA only)

0/4 - 20mA (load max. 270 Ohm)

0 - ±10V (load max. 2 mA)

Resolution 14 bits, Accuracy 0.1%

Response time < 1 msec. (a) 

 Ambient temperature

Operation: 0-45°C (32 - 113°F)

Storage: -25 - +70°C (-13 - 158°F) 

Housing   Norly UL94 - V - 0  
 Display 6 Digit, LED, high-efficiency red, 15mm (0.59") 
 Protection class rear side IP20 
 Screw Terminals Cross section max. 1.5mm² 
 Conformity and Standards EMC 2004/108/EC: EN61000-6-2, EN61000-6-3; LV2006/95/EC: EN61010-1 
(a) Continuous serial communication may termporary increase response times; Overal response  = measuring time + response time  
(b) Diode or RC filtering is mandatory when switching inductive loads