We have multiple autoclaves with a small motor where we need to read and control the speed. We use a Honeywell optical sensor, and we used to have it set up with a SNAP-AIRATE card that would read the input in Hertz. We double checked it’s still working on the SNAP set-up, and so the sensor is fine. However, we wired it to a grv-PR-1 MM-1001-10 card, and set it up in PAC Control as DI: 5-30 VDC, Feature: Frequency, but can’t get it to give a reading.
There is a 4.7kOhm resistor and a 5V DC power supply.
Also, the PR-1 is 4.1.2-b.155, the card firmware is R1.32d, so those are both up to date.
What am I missing to make it work? I tried to leave it without a “Feature”, but then using the Command “GetFrequency” gave an error message.
The Frequency function of the GRV-MM1001-10 is not a direct one-to-one replacement for the SNAP-AIRATE, which is a dedicated Frequency Input Module.
What are the electrical details for your optical sensor that provides the electrical signal to be wired to the input? Is it PNP / NPN / Push-Pull / Open Collector?
The electrical input requirements, maximum frequency, and frequency accuracy are different.
The most important difference: Frequency range
The SNAP-AIRATE is a dedicated frequency input module.
Typical specifications include:
Frequency range: 0–25 kHz
Overrange capability: up to approximately 27.5 kHz
Resolution: 1 Hz
Designed specifically for frequency measurement
The GRV-MM1001-10, on the other hand, implements frequency measurement as one of the functions of its Discrete Counter Input.
For the Frequency/Period function, the relevant specification is:
Input voltage: 5–30 VDC
ON threshold: approximately 5 V
OFF threshold: approximately 1.5 V
Maximum frequency for Frequency/Period measurement: 2 kHz
A typical example where the GRV-MM1001-10 can be a replacement. Suppose your existing application is:
Sensor: 24-V PNP pulse output
Frequency: 0–500 Hz
Application: Speed monitoring
Required accuracy: ±1%
Please check the specs of the current setup with the SNAP-AIRATE, and compare them with the specs of the GRV-MM1001-10, configured as a Discrete Input. It may need signal conditioning or use of a different sensor.
Yah, that is why we still use a lot of SNAP stuff…although Epic has the right input available, you may have to buy a whole card of specific inputs you only need one of and don’t otherwise need.
Your options are:
Buy a whole 12 or 24 input card to match the specs of your sensor.
If you have a serial input card on the Epic and an open serial channel, you can use TTL logic and some scripting to turn a serial input into a speed value.
Buy a sensor with Modbus RTU output and either use a USB or Epic card.
Keep the Snap brain/R1/R2, and treat as brain with Epic.
If I see an application like this and I am trying to upgrade the ap for some reason of data connectivity or Ignition, or whatever, I’ll think twice before replacing the snap hardware when I can just add an Epic to the mix and keep everything original that was working.
